Micro-channel-cooled high heat load light emitting device

ABSTRACT

Micro-channel-cooled UV curing systems and components thereof are provided. According to one embodiment, a lamp head module includes an optical macro-reflector, an array of LEDs and a micro-channel cooler assembly. The array is positioned within the reflector and has a high fill factor and a high aspect ratio. The array provides a high irradiance output beam pattern having a peak irradiance of greater than 25 W/cm 2  at a work piece surface at least 1 mm away from an outer surface of a window of the reflector. The micro-channel cooler assembly maintains a substantially isothermal state among p-n junctions of the LEDs at less than or equal to 80° Celsius. The micro-channel cooler assembly also provides a common anode substrate for the array. A thermally efficient electrical connection is formed between the array and the common anode substrate by mounting the array to the micro-channel cooler assembly.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority to U.S. Utility patentapplication Ser. No. 13/014,069, filed on Jan. 26, 2011, now U.S. Pat.No. 8,378,322; U.S. Provisional Patent Application No. 61/336,979, filedon Jan. 27, 2010; U.S. Provisional Patent Application No. 61/341,594,filed on Apr. 1, 2010; and U.S. Provisional Patent Application No.61/456,426, filed on Nov. 5, 2010, all of which are hereby incorporatedby reference in their entirety for all purposes.

COPYRIGHT NOTICE

Contained herein is material that is subject to copyright protection.The copyright owner has no objection to the facsimile reproduction ofthe patent disclosure by any person as it appears in the Patent andTrademark Office patent files or records, but otherwise reserves allrights to the copyright whatsoever. Copyright© 2010-2011, Fusion UVSystems, Inc.

BACKGROUND

1. Field

Embodiments of the present invention generally relate to light emittingdiodes (LEDs) on low thermal resistance substrates. In particular,embodiments of the present invention relate to high power density, highfill-factor, micro-channel-cooled ultraviolet (UV) LED lamp head modulesthat provide high brightness, high irradiance and high energy density.

2. Description of the Related Art

Today's UV LEDs remain relatively inefficient (typically, operating atabout 15% efficiency when operated at high current densities). Theseinefficiencies result in the production of large quantities of wasteheat and therefore requiring at least air cooling and often liquidcooling (e.g., heat exchangers and/or chillers) to remove the unwantedwaste heat, which is a by-product of the electrical to opticalconversion process within the p-n junction of the semiconductor device.If the heat is not removed in a very effective and efficient manner, theLED devices may suffer loss of efficiency, decrease in light output andeven catastrophic failure.

Liquid-cooled UV LED lamps (or light engines) are currently being usedin a variety of curing applications; however, existing systems haveseveral limitations. For example, while industry literature acknowledgesthe desirability of high brightness/high irradiance arrays, currentlyavailable UV LED lamps provide sub-optimal performance. Existing UV LEDlamps generally tend to electrically connect the LEDs within their LEDarrays in strings of series-connected LEDs and then parallel thesestrings together (often with integrated resistors). One drawback to thisseries-parallel methodology is that the heat sinks usually have to be ofa non-electrically conductive nature and/or there needs to be adielectric layer underneath the LED(s), either of which is traditionallypatterned with electrically conductive circuit traces. These traces areexpensive and incompatible with thermally efficient ultra-high currentoperation because of the contact thermal resistance of the layersinvolved and/or the bulk thermal resistance of the dielectric layerand/or the inherently high electrical resistivity of traces. The heatsinks are also often of expensive ceramic materials such as BeO, SiC,AlN, or alumina. Another disadvantage to the series-parallel LED arraymodel is that a single failure of an LED can lead to the failure of thewhole string of seriesed LED(s). This dark area created by a failure inany given chain of LEDs is usually detrimental to the process where thelight photo-chemically interacts at the work piece surface.

A specific example of a prior art UV LED array is illustrated in FIGS.1A and 1B. In this example, which is taken from US Pub. No 2010/0052002(hereafter “Owen”), an alleged “dense” LED array 100 is depicted forapplications purported to require “high optical power density”. Thearray 100 is constructed by forming micro-reflectors 154 within asubstrate 152 and mounting an LED 156 within each micro-reflector 154.The LEDs 56 are electrically connected to a power source (not shown)through a lead line 158 to a wire bond pad on substrate 152. Themicro-reflectors 154 each include a reflective layer 162 to reflectlight produced by the associated LED 156. Notably, despite beingcharacterized as a “dense” LED array, LED array 100 is in reality a verylow fill-factor, low brightness, low heat flux array in that theindividual LEDs 156 are spaced quite some distance apart having acenter-to-center spacing of about 800 microns. At best, it would appearthe LEDs account for approximately between 10 to 20% of the surface areaof LED array 100 and certainly less than 50%. Such low fill-factor LEDarrays can create an uneven irradiance pattern which can lead to unevencuring and visually perceptible anomalies, such as aliasing andpixelation. Additionally, the micro-reflectors 154 fail to capture andcontrol a substantial amount of light by virtue of their low angularextent. Consequently, array 100 produces a low irradiance beam thatrapidly loses irradiance as a function of the distance from thereflector 154. It is to be further noted that even optimally configuredreflectors would not make up for the low brightness of LED array 100 asthe ultimate projected light beam onto the work piece can never bebrighter than the source (in this case LED array 100). This is due tothe well-known conservation of brightness theorem. Furthermore, Owenalso teaches away from the use of macro-reflectors due to their size andthe perceived need to have a reflector associated with each individualLED 156.

The aforementioned limitations aside, the relatively large channelliquid cooling technology employed in prior-art cooling designs is notcapable of removing waste heat from the LEDs in a manner that would beeffective in keeping junction temperatures adequately low when thecurrent per square millimeter exceeds approximately 1.5 amps.

Oxygen inhibition is the competition between ambient oxygen reactingwith the cured material at a comparable rate as the chemicalcross-linking induced by the UV light and photoinitiator (PhI)interaction. Higher irradiance is known to create thorough cures morerapidly and higher irradiance is known to at least partially addressoxygen inhibition issues. Ultra high irradiance is now thought toperhaps overcome oxygen inhibition issues in certain processconfigurations perhaps even without a nitrogen cover gas. However, toproduce ultra high irradiance to overcome oxygen inhibition, the heatflux removal rate needed to keep junction temperatures adequately low insuch a high fill-factor LED array environment operating at extremelyhigh current densities and is simply not attainable with currentlyemployed UV LED array architectures and UV LED array coolingtechnologies.

SUMMARY

Micro-channel-cooled UV curing systems and components thereof aredescribed that are configured for photo-chemical curing of materials andother high-brightness/high-irradiance applications. According to oneembodiment, a lamp head module includes an optical macro-reflector, anarray of light emitting diodes (LEDs) and a micro-channel coolerassembly. The optical macro-reflector includes a window having an outersurface. The array is positioned within the optical reflector and has ahigh fill factor and a high aspect ratio. The array is operable toprovide a high irradiance output beam pattern having a peak irradianceof greater than 25 W/cm² at a work piece surface at least 1 mm away fromthe outer surface of the window of the optical reflector. Themicro-channel cooler assembly is operable to maintain a substantiallyisothermal state among p-n junctions of the LEDs in the array at atemperature of less than or equal to 80° Celsius. The micro-channelcooler assembly also provides a common anode substrate for the array. Athermally efficient electrical connection is formed between the arrayand the common anode substrate by mounting the array to themicro-channel cooler assembly.

In the aforementioned embodiment, the array may be directly mounted tothe micro-channel cooler assembly.

In various of the aforementioned embodiments, the micro-channel coolerassembly may maintain a substantially isothermal state among the p-njunctions at a temperature of substantially less than or equal to 45°Celsius.

In the context of various of the aforementioned embodiments, the LEDsmay be electrically paralleled.

In some instances of the aforementioned embodiments, at least one of theLEDs may be an ultraviolet emitting LED.

In various of the aforementioned embodiments, an aspect ratio of a widthto a length of the array is substantially between approximately 1:2 to1:100.

In various of the aforementioned embodiments, an aspect ratio of thewidth to the length of the array is approximately 1:68.

In the context of various of the aforementioned embodiments, the peakirradiance may be greater than or equal to 100 W/cm² and the work piecesurface is at least 2 mm away from the outer surface of the window ofthe optical reflector.

In various of the aforementioned embodiments, no significant number ofthe LEDs is connected in series.

In some instances of the aforementioned embodiments, coolant flowthrough the micro-channel cooler across and underneath the array isconfigured to be in a direction substantially parallel to a shortestdimension of the array and may additionally be substantially balanced.

In various of the aforementioned embodiments, the lamp head module mayinclude a flex-circuit, operable to individually address the LEDs orgroups of the LEDs, bonded to the micro-channel cooler.

In the context of various of the aforementioned embodiments, themicro-channel cooler may be clamped between one or more cathodeconnectors and one or more anode bus bodies to facilitate factoryreplaceability.

In various of the aforementioned embodiments, the lamp head module mayinclude integrated LED drivers.

In some instances of the aforementioned embodiments, the opticalmacro-reflector may be field replaceable.

Other embodiments of the present invention provide an ultraviolet (UV)light emitting diode (LED) curing system including multiple end-to-endserially connected UV LED lamp head modules each including an opticalmacro-reflector, an LED array and a micro-channel cooler assembly. Theoptical macro-reflector includes a window having an outer surface. TheLED array is positioned within the optical reflector and has a high fillfactor and a high aspect ratio. The LED array is operable to provide asubstantially uniform high irradiance output beam pattern having anirradiance of greater than 25 W/cm² at a work piece surface at least 1mm away from the outer surface of the window of the optical reflector.The micro-channel cooler assembly is operable to maintain asubstantially isothermal state among p-n junctions of the LEDs in theLED array at a temperature of less than or equal to 80° Celsius. Themicro-channel cooler assembly also provides a common anode substrate forthe LED array. A thermally efficient electrical connection is formedbetween the LED array and the common anode substrate by directlymounting the LED array to the micro-channel cooler assembly.

Other features of embodiments of the present invention will be apparentfrom the accompanying drawings and from the detailed description thatfollows.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention are illustrated by way of example,and not by way of limitation, in the figures of the accompanyingdrawings and in which like reference numerals refer to similar elementsand in which:

FIG. 1A is a top view of a portion of a prior art LED array.

FIG. 1B is a view of the LED array of FIG. 1A taken along section line1B-1B.

FIG. 2A is an isometric view of a UV LED lamp head module in accordancewith an embodiment of the present invention.

FIG. 2B is a front view of the UV LED lamp head module of FIG. 2A.

FIG. 2C is a side view of the UV LED lamp head module of FIG. 2A.

FIG. 3A is a top-level isometric cut-away view of the UV LED lamp headmodule of FIGS. 2A-C.

FIG. 3A is a top-level isometric cut-away view of the UV LED lamp headmodule of FIG. 2A.

FIG. 3B is a top-level front cut-away view of the UV LED lamp headmodule of FIG. 2A.

FIG. 3C is a top-level isometric exploded view of the UV LED lamp headmodule of FIG. 2A.

FIG. 4A is a magnified isometric cut-away view of a bottom portion of areflector and a top portion of a body of the UV LED lamp head module ofFIG. 2A.

FIG. 4B is a magnified front cut-away view of a bottom portion of areflector and a top portion of a body of the UV LED lamp head module ofFIG. 2A.

FIG. 5A is a further magnified isometric cut-away view illustrating anLED array and its interface with a common anode substrate layer of theUV LED lamp head module of FIG. 2A.

FIG. 5B is a further magnified front cut-away view illustrating an LEDarray and its interface with a common anode substrate layer of the UVLED lamp head module of FIG. 2A.

FIG. 6 is an exploded magnified isometric cut-away view of a top portionof a body of and illustrating various layers of the UV LED lamp headmodule of FIG. 2A.

FIG. 7 is an exploded magnified isometric cut-away view of a top portionof a reflector of the UV LED lamp head module of FIG. 2A.

FIG. 8 is a magnified isometric view of a reflector of the UV LED lamphead module of FIG. 2A with the end cap removed.

FIG. 9A and FIG. 9B are an isometric view and an exploded isometricview, respectively, of four interconnected UV LED lamp head modules inaccordance with an embodiment of the present invention.

FIG. 10A is an isometric view of an alternative embodiment of an LEDarray package and heat spreader.

FIG. 10B is an isometric view of an alternative embodiment of an LEDarray package and heat spreader with a macro-reflector in accordancewith an embodiment of the present invention.

FIG. 10C is an isometric view depicting the bottom-side of the heatspreader of FIGS. 10A and 10B.

FIG. 10D is an isometric cut-away view of an alternative embodiment of aUV LED lamp head module.

FIG. 10E is a front cut-away view of yet another alternative embodimentof a UV LED lamp head module.

FIG. 10F is a magnified isometric cut-away view of the UV LED lamp headmodule of FIG. 10E.

FIG. 10G is a further magnified isometric cut-away view of the UV LEDlamp head module of FIG. 10E.

FIG. 11A conceptually illustrates two macro-reflectors of substantiallythe same height for different working distances in accordance with anembodiment of the present invention.

FIG. 11B is a magnified view of FIG. 11A illustrating marginal rays fora 2 mm macro-reflector in accordance with an embodiment of the presentinvention.

FIG. 12 shows a macro-reflector optimized for a 2 mm focal plane inwhich each side of the reflector has a focal point that is offset fromthe centerline of the focused beam on the work piece in accordance withan embodiment of the present invention.

FIG. 13 is a graph illustrating estimated convective thermal resistancefor various channel widths.

FIG. 14 is a graph illustrating output power for various junctiontemperatures.

FIG. 15 is a graph illustrating a dynamic resistance vs. forward currentcurve.

FIG. 16 is a graph illustrating an irradiance profile for a UV LED lamphead with a reflector optimized for a 2 mm focal plane in accordancewith an embodiment of the present invention.

FIG. 17 is a graph illustrating an irradiance profile for a UV LED lamphead with a reflector optimized for a 53 mm focal plane in accordancewith an embodiment of the present invention.

DETAILED DESCRIPTION

Micro-channel-cooled UV curing systems and components thereof aredescribed that are configured for photo-chemical curing of materials andother applications requiring high fill-factor, high current density andhigh-brightness attributes (which ultimately leads to the attribute ofhigh-irradiance). According to one embodiment of the present invention,LEDs of a high fill factor LED array of an ultra high irradiance UVcuring system are placed substantially in electrical parallel (a/k/amassively parallel) on a common anode substrate to achieve a verythermally efficient manner of connection (e.g., with no thermallyimpeding dielectric layer between the base of the LEDs and the substrateas is typically required in a series configuration or a series/parallelconfiguration).

According to embodiments of the present invention, in order toaccommodate the heat flux/thermal demands of a high fill-factor, highcurrent density and high-brightness UV LED lamp head module, practicalmeans to achieve isothermal common anode substrate behavior, even whenthe common anode substrate has a very high aspect ratio, are alsoprovided. According to one embodiment, an LED array is directly bondedto a micro-channel cooler and the coolant flows across and underneaththe LED array in a direction substantially parallel to the shortestdimension of the LED array. In one embodiment, coolant flow throughmicro-channels running beneath the LEDs is approximately equal (e.g.,balanced) so that the p-n junctions of the LEDs of the LED array aresubstantially isothermal. In one embodiment, the high aspect ratiocommon anode substrate is substantially isothermal from side to side andend to end. This may be achieved through the use of a preferablysubstantially copper micro-channel cooler having micro-channels thatdirect the coolant flow under the LED array in a substantially lateraldirection to the longitudinal axis of the LED array, while maintaining atight flow balance range between each channel. In one embodiment, thisflow balance is achieved by designing the primary coolant inlet and exitcoolant fluid channels that run parallel to the longitudinal axis of theLED array to reach a level of pressure drop that is nearly homogeneousalong their length.

In various embodiments, a flex-circuit, bonded to a micro-channelcooler, is used to individually address LEDs or groups of LEDs of an LEDarray so that the LEDs may be binned for forward voltage (Vf),wavelength, size, optical power, etc., thereby substantially loweringthe demands on the LED manufacturer(s) to supply LED groups in just oneor a few bins. This also allows the UV LED lamps of embodiments of thepresent invention to use multiple bins of LEDs This ability to usemultiple bins of LEDs enhances the ability to manufacture UV LED lampsthat do not require binning in and of themselves.

In some embodiments, a monolithic micro-channel cooler is employed thatis factory replaceable, or otherwise known as a consumable part. Asdescribed further below, while the LEDs and flex-circuit may be bondedto the top surface of the micro-channel cooler, and thereforeessentially considered to be permanently affixed, the micro-channelcooler assembly is uniquely clamped (e.g., with screws providing theclamping force) between various geometrically configured cathodemicro-bus bars and/or connectors (e.g., rectangular, claw and the like)and various geometrically configured preferably monolithic anode busbody (e.g., rectangular, plate and the like), thereby facilitatingreplaceability.

According to various embodiments of the present invention, the UV LEDlamp head module may include integrated LED drivers. In this manner, offthe shelf AC/DC power supplies designed for high volume “server farms”may be used and a 12V power cable can be run to the UV LED lamp headmodule (e.g., UV LED lamp head module 200) rather than remotelyperforming DC/DC and running a larger diameter (smaller gage) 5V powercable to the UV LED lamp head module. In embodiments in which integratedhigh power density LED drivers are utilized, they can be mounted to themain lamp body with an intervening thermal conduction compound ormonolithic interface material in order to transfer and/or dissipate thewaste heat from the driver assemblies into the body where the waste heatis carried off by the same coolant flow that cools the LED array.

In some embodiments, factory and/or field replaceable macro-reflectorsare employed, which may be customized for particular applications byproviding different performance characteristics (e.g., high-irradiance,highly focused; short working distances to focused, long workingdistances; applications requiring large depth of focus while maintaininghigh-irradiance; and very wide-angle, more uniform irradianceapplications).

In the following description, numerous specific details are set forth inorder to provide a thorough understanding of embodiments of the presentinvention. It will be apparent, however, to one skilled in the art thatembodiments of the present invention may be practiced without some ofthese specific details.

Notably, while embodiments of the present invention may be described inthe context of UV LED systems, embodiments of the present invention arenot so limited. For example, visible and IR applications arecontemplated and would benefit from the architectural improvementsdescribed herein. Also, varying wavelengths can be used within the samelight emitting device lamp to mimic the output of mercury lamps by usingUV A, B or C light emitting devices and visible and/or IR light emittingdevices. The high fill-factor characteristic of embodiments of thepresent invention also enables inter-disbursement of the variouswavelengths while avoiding pixelation effects on the work piece surfacewhich would likely result in deleterious process effects. Further, inaccordance with various embodiments, the wavelength mixing within themacro-non-imaging-optical reflectors result in a uniform (non-pixelated)output beam from both a power density and wavelength mixing standpoint.

For sake of brevity, embodiments of the present invention may bedescribed in the context of LEDs having the anode side on the bottom,those of ordinary skill in the art will recognize that the anode sidecould be on the top surface and/or both anode and cathode contacts couldbe on the top or the bottom. As such, references to anodic/cathodicstructures herein could be or could be reversed (or could beelectrically neutral) depending upon the particular implementation.Similarly, flip chip no wire bond LEDs, conductive substrate andnon-conductive substrate LED chips (such as those with the EPI layer onsapphire, aluminum nitride, silicon or zinc oxide), arrays and/orpackaged devices may be considered. The EPI layer could be selected fromthe group of nitrides, oxides, silicon, carbides, phosphides, arsenides,etc.).

Terminology

Brief definitions of terms used throughout this application are givenbelow.

The phrase “average irradiance” generally refers to the irradiance valueacross a width of an output beam pattern projected on a work piecewherein the irradiance value falls to essentially zero on each side ofthe output beam pattern. In embodiments of the present invention, at 2mm from the window, a UV LED lamp head module produces averageirradiance of approximately 32 W/cm² (range 40-80 W/cm²). In embodimentsof the present invention, at 53 mm from the window, a UV LED lamp headmodule produces average irradiance of approximately 6 W/cm² (range 8-15W/cm²).

The terms “connected,” “coupled,” “mounted” and related terms are usedin an operational sense and are not necessarily limited to a directconnection, coupling or mounting.

The phrase “diffusion bonding” generally refers to a method of joiningmetals similar to welding, but relies only on the surface diffusing intoone another as a means of “welding.” For example a diffusion bondingprocess may bond layers of usually substantially similar materials byclamping them together, sometimes with an oxidation inhibiting platingsuch as nickel, and subjecting the layers to extremely high temperaturesof around 1,000 degrees C. (range 500-5,000 degrees C.), and therebymolecularly intermixing the surfaces and forming a substantiallymonolithic material wherein the grains are intermixed and often thebond-line is substantially indistinguishable from the bulk material, andthe properties of the diffusion bonded materials do not differsubstantially from bulk non-diffusion bonded materials in terms ofthermal conductivity and strength. Diffusion bonding could have somesimilarities to sintering. Thin layers of silver plating on the order ofmicrons may also be employed to facilitate the ease of bonding of thelayers. This later process may have some similarities to soldering.

The phrase “directly mounted” generally refers to a mounting in which nosubstantial intervening and/or thermally impeding layer is introducedthe two things being attached or affixed. In one embodiment, an LEDarray is mounted to a common anode substrate provided by a surface of amicro-channel cooler with a thin solder layer. This is an example ofwhat is intended to be encompassed by the phrase “directly mounted.” So,the LED array would be considered to be directly mounted to the commonanode substrate. Examples of thermally impeding layers would includebulk substrate material, foil, thin-film (dielectric or conducting), orother material (other than a thin solder layer) introduced between thetwo things being attached or affixed.

The phrase “high irradiance” generally refers to an irradiance ofgreater than 4 W/cm². According to embodiments of the present invention,peak irradiance levels achievable are approximately ten times the levelsof current state-of-the-art UV LED curing systems while maintaining bothhigh efficiency and long life of the LEDs. As described further below,in accordance with various embodiments, the irradiance on the work pieceis substantially devoid of deleterious pixelation and/or gaps found incurrent UV LED curing systems. Meanwhile, it is to be noted most UV LEDlamp manufacturers measure peak irradiance at the window, whereas invarious embodiments described herein it is measured at the work piecesurface. Measurements at the window are essentially meaningless as thework piece is not typically located at the window.

The phrase “high fill-factor LED array” generally refers to an LED arrayin which the LEDs are closely spaced and exceed 50% (often exceeding90%) of the surface area of the LED array. In one embodiment of thepresent invention, LEDs within LED arrays are spaced less than 20microns edge-to-edge and in some instances 10 microns edge-to-edge, witha range of edge-to-edge distances from 1-100 microns (zero micronspacing could be considered for a completely monolithic LED). Bothinorganic as well as substantially organic LEDs are contemplated.

The phrases “in one embodiment,” “according to one embodiment,” and thelike generally mean the particular feature, structure, or characteristicfollowing the phrase is included in at least one embodiment of thepresent invention, and may be included in more than one embodiment ofthe present invention. Importantly, such phases do not necessarily referto the same embodiment.

The term “irradiance” generally refers to the radiant power arriving ata surface per unit area (e.g., watts or milliwatts per square centimeter(W/cm² or mW/cm²).

The phrase “light emitting device” generally refers to one or more lightemitting diodes (LEDs) (emitting substantially incoherent light) and/orlaser diodes (emitting substantially coherent light) whether they beedge emitters or surface emitters. In various embodiments of the presentinvention, light emitting devices may be packaged or bare dies. Apackaged die refers to a device that not only consists of the bare die,but usually also consists of a substrate to which the die is mounted(usually soldered) to facilitate the traces for electrical in and outcurrent paths, as well as thermal paths, and usually a means forattaching a lens and/or reflectors, an example of which would be theLexeon Rebel available from Philips, USA. According to one embodiment,bare light emitting device dies (i.e., dies excised directly from wafersthat have epitaxial grown p-n junctions) are bonded (usually soldered)directly (without an additional significantly thermally impeding layer)to at least one diffusion bonded layer of a high thermal conductivitymaterial (selected from the group of copper, Glidcop, BeO, AlN, Al₂O₃,Al, Au, Ag, graphite, diamond and the like), which is in itself, invarious embodiments of the present invention, usually a layer of amulti-layer laminate forming a monolithic diffusion bonded micro-channelcooler structure. The laminate does not necessarily have to be diffusionbonded as the bonding process could be selected from soldering, brazing,gluing, etc.

The phrase “light emitting diode” or the acronym “LED” generally referto a semiconductor device containing a p-n junction (the junctionbetween a p-type semiconductor and an n-type semiconductor) designed toemit specific narrow band wavelengths within the electromagneticspectrum via a process known as electroluminescence. In one embodiment,an LED emits incoherent light.

The phrase “low fill-factor LED array” generally refers to an LED arrayin which the LEDs are sparsely arranged and do not exceed approximately50% of the surface area of the LED array.

The phrase “low irradiance” generally refers to an irradiance of around20 W/cm² or less. UV LED systems rated at less than 4 W/cm² are nottypically sufficient for most curing applications other than pinning(e.g., ink setting).

The term “macro-reflector” generally refers to a reflector having aheight of greater than or equal to 5 mm. In some embodiments,macro-reflectors may range from 5 mm to over 100 mm.

If the specification states a component or feature “may”, “can”,“could”, or “might” be included or have a characteristic, thatparticular component or feature is not required to be included or havethe characteristic.

The phrase “peak irradiance” generally refers to the maximum irradiancevalue across a width of an output beam pattern projected on a workpiece. In embodiments of the present invention, at 2 mm from the window,a UV LED lamp head module can achieve a peak irradiance of approximately84 W/cm² (range 50-100 W/cm²). In embodiments of the present invention,at 53 mm from the window, a UV LED lamp head module can achieve a peakirradiance of approximately 24 W/cm² (range 10-50 W/cm²).

The phrases “radiant energy density,” “total output power density” or“energy density” generally refer to the energy arriving at a surface perunit area (e.g., joules or millijoules per square centimeter (J/cm² ormJ/cm²)).

The term “responsive” includes completely or partially responsive.

The phrase “total output power” generally refers to the aggregate powerin W/cm of output beam pattern length. According to one embodiment, at 2mm from the window, total output power of approximately 20.5 W per cm ofoutput beam pattern length is produced by each UV LED lamp head module.According to one embodiment, at 53 mm from the window, total outputpower of approximately 21.7 W per cm of output beam pattern length isproduced by each UV LED lamp head module.

The phrase “ultra high irradiance” generally refers to an irradiance ofgreater than 50 W/cm² at a work piece. In one embodiment, a UV LED lamphead module can achieve peak irradiance of greater than 100 W/cm² atshort working distances (e.g., ˜2 mm). In view of rapidly advancingpower output and efficiency of LEDs, it is reasonable to expect peakirradiances achievable to improve by more than an order of magnitude inthe coming decades. As such, some of today's high irradianceapplications will be accomplished with air-cooled LED arrays and otherswill take advantage of or be enabled by these higher irradiances forfaster, harder or more complete cures and/or use less photoinitiator.Also unique in the context of various embodiments of the presentinvention is the ability to provide both ultra high peak irradiance,ultra high average irradiance, ultra high total irradiance (dose) andconcentration of the dose (as compared to the prior art) that isdelivered to the work piece.

The phrase “UV curing process” generally refers to a process in which aphotoinitiator (PhI) will absorb UV light first, causing it to go in toan excited state. From the excited state, PhI will decompose into freeradicals, which then starts a photo polymerization. However, there isalways some amount of oxygen (1-2 mM) in the UV curable formulation.Therefore, the initial free radicals from PhI photo-decomposition willreact with oxygen first, instead of reacting with the monomer's doublebond of (typically an acrylate), because the reaction rate of PhI freeradical with oxygen is about 105 to 106 faster than that of the acylatedouble bonds. Furthermore, at very early stages of UV curing, oxygen inair will also diffuse into the cured film and also react with the PhI,which results in major oxygen inhibition. Only after the oxygen in UVcurable film is consumed can photo-initiated polymerization take place.Therefore, in order to overcome oxygen inhibition, a large amount offree radicals are required at surface of the cured film within a veryshort period of time; i.e. a high intensity UV light source is required.The absorption of the UV light intensity for a particular formulationdepends on the UV light wavelength. Mathematically, the absorbed UVlight intensity (Ia) is given by Ia=I0×[PhI], where I0 is a UV lightintensity from UV light source and [PhI] is photoinitiatorconcentration. At the same [PhI] levels, increasing I0 will increase Iaand thereby reduce oxygen inhibition. Stated another way, by using ahigh I0 light source less [PhI] can used, which is typically the mostexpensive portion of the formulation. The absorption of UV light followsthe well-known Lambert-Beer Law: A (absorption)=

cd, where

is the PhI extinction or absorption coefficient, c is the concentrationof PhI and d is the thickness of the sample (film to be cured). As seenfrom the below table, the efficiency of PhI light absorption variesgreatly with wavelength. In this case, at 254 nm, the efficiency ofabsorbing light is 20 times higher than that at 405 nm. Therefore, ifthe UV LED light intensity at 400 nm can be provided at 100 timestypical curing powers at shorter wavelengths (˜100 W/cm²), thephotoinitiator's efficiency difference in absorption of light can reduceoxygen inhibition.

1.95×104 at 254 nm,

1.8×104 at 302 nm,

1.5×104 at 313 nm,

2.3×103 at 365 nm,

8.99×102 at 405 nm;

FIGS. 2A-C provide isometric, front and side views, respectively, of anultra-high brightness UV LED lamp head module 200 in accordance with anembodiment of the present invention. According to one embodiment,ultra-high brightness UV LED lamp head module 200 produces ultra-highirradiance. Ultra-high brightness UV LED lamp head module 200 may beused to, among other things, photo polymerize, or cure inks, coatings,adhesives and the like. Depending upon the application, a UV curingsystem (LED UV emitting system) (not shown) may be formed comprising oneor more UV LED lamp head modules 200 and other components, including,but not limited to, LED drivers (internal or external to the UV LED lamphead module 200), one or more cooling systems, one or more main AC/DCpower supply systems (e.g., available from Lineage USA or Power-One,USA, which are approximately 90% (or more) efficient and weighing about1 kg.), one or more control modules, one or more cables and one or moreconnectors (not shown).

According to one embodiment, the high brightness of UV LED lamp headmodule 200 allows a range of possible optical properties of the outputbeam (not shown) including: narrow width (e.g., ˜0.65 cm (range 0.1 to 2cm)) with high power density (e.g., ˜20.5 W per cm of output beampattern length (range 10-30 W)), wider widths (e.g., ˜3.65 cm (range 3to 10 cm) with greater depth of focus, or short or long workingdistances (with or without greater depth of focus), or even very wideangle/large area beam output patterns (with or without greater depth offocus). Output beam patterns with homogenous irradiance across the widthof the beam (as well as the length of the beam) pattern may beconsidered.

As discussed further below, according to embodiments of the presentinvention, the high brightness results from a high fill-factor (inexcess of 50%, and often in excess of 90%) LED array (not shown) and theLED array being operated at high electrical power densities, whichresults in a high irradiance output beam. The high electrical powerdensities result in high thermal densities (due to electrical to opticalconversion loses) that are effectively managed via various novelmethodologies that are described in detail below.

Ultimately, the UV LED lamp head module 200 is intended to replace notonly the current state-of-the-art UV LED lamps, but also the currentstate-of-the-art mercury lamps, due to the uniquely high irradiance andflexible optical output beam properties that a high brightness sourceallows. UV LED lamp head module 200 is also considered to be a “greentechnology” as it contains no mercury, and is also electrically veryefficient. This efficiency is partly derived from the inherentefficiency of LEDs compared to mercury containing lamps, but alsoderived in part from cooling methodologies, which are described below,that provide for very low thermal resistance between the LED junctionsand the cooling fluid (introduced into the UV LED lamp head module 200via inlet cooling tube 203 and evacuated from the UV LED lamp headmodule 200 via outlet cooling tube 204), thereby creating low junctiontemperatures that are needed for highly efficient operation of LEDdevices.

In this depiction, a housing 202 and a reflector 201 of the UV LED lamphead module 200 are illustrated. According to various embodiments, thehousing 202 of the UV LED lamp head module 200 is approximately 80 mm inlength×38 mm in width×125 mm in height. The length of the novel easilyswappable and field-replaceable reflector 201 that is chosen for a givenapplication would be substantially in the range of tens to hundreds ofmillimeters in length, but such reflectors are typically about 100 mm inlength, and provide working distances in the range of 0-1000 mm, buttypically 2 mm to 53 mm.

According to embodiments of the present invention, UV LED lamp headmodule 200 is designed to be used stand alone or serially in combinationwith one or more other UV LED lamp head modules. As described furtherbelow, multiple UV LED lamp head modules 200 are easily configuredserially in length from one head (module) (e.g., 80 mm), to perhaps 100heads (modules), for example, with a length of 8,000 mm. Multiple UV LEDlamp head modules 200 could also be configured serially in width.According to one embodiment, a unique feature of a length-wise serialcombination of UV LED lamp head modules 200 is that the output beam doesnot contain a substantially discernable loss of irradiance at eachinterface point at which the heads (modules) are butted up against eachother serially end-to-end to make a long output beam pattern at the workpiece surface even in short working distance (e.g., ˜2 mm) applications.

As described in further detail below, in one embodiment, reflector 201is factory swappable and preferably also field replaceable. Thereflector 201 may be machined from aluminum and polished, cast, extrudedmetallic or polymer, etc., or injection molded. The reflector 201 couldhave silver coatings and could have a dielectric stack of coatings. Thereflector 201 could have a single layer protective dielectric coatingusing deposition processes (e.g., ALD, CVD, sputtering, evaporation,sol-gel). The reflector 201 could be mechanically or electrolyticallypolished. It is contemplated that multiple UV LED lamp head modules 200may often need to be placed end-to-end in long length applications, likewide-format printing. In these cases, it is desirable that the projectedand/or focused beam created by the reflector 201 has nearly uniformirradiance along the entire beam path, especially in the areas betweenthe end-to-end configured UV LED lamp head modules 200 and/or LEDarrays, so that the coatings, inks, adhesives, etc. of the work pieceare uniformly cured. It should be noted that due to the high irradiancesprovided by embodiments of the present invention coating and inks, etc.may have substantially less photoinitiator in them or essentially nophotoinitiator and cure in a similar matter to E-beam in thatelectromagnetic energy is supplied in a sufficient dose to cure thematerial without the aid of any appreciable photoinitiator.

In various embodiments, the irradiance of the UV LED lamp head module200 can be in excess of 100 W/cm2 in short working distance (e.g., ˜2mm) applications, such as inkjet printing, to in excess of 25 W/cm2 inlong working distance (e.g., 50 mm+) applications, such as clear coatcuring. According to one embodiment, the beam widths can vary, to meet avariety of applications and operating conditions, from around 1 mm wideto 100 mm wide or more, and the length, as stated previously can be asshort as the width of one head (module) (e.g., 80 mm) to as long as 100heads (modules) (e.g., 8,000 mm) or more. It should be noted that thelength of the beam could be shorter than the length of the UV LED lamphead module 200 if focusing reflectors or optics were so employed toaffect this beam shape. External refractive or defractive optics arealso contemplated. Depending upon the particular implementation, thelength of the UV LED lamp head module 200 could range from tens tohundreds of millimeters in length. The LEDs could range fromapproximately 0.3 mm² to 4 mm² or more and they could be rectangular,oriented in single long rows, multiple long rows or monolithic.

According to embodiments of the present invention, the efficiency of theLED array 330 is usually well in excess of 10-20%, and the overallsystem efficiency (including heat exchanger or chiller, pump, and powersupply losses, is usually well in excess of 5-10%).

Returning briefly to the inlet cooling tube 203 and the outlet coolingtube 204, these may constructed of, for example, extruded polyurethane,vinyl, PVC (available from Hudson Extrusions, USA) and the like andcould be ˜ 5/16 inch ID and ˜ 7/16 inch OD. In one embodiment, the tubes203 and 204 are of a polyurethane with high tensile strength and lowmoisture absorption. Tube fittings available from Swagelok, USA may beemployed or fittings from John Guest, USA. Depending upon the usageenvironment, it may be preferable to use more than one inlet coolingtube 203 and outlet cooling tube 204, such as perhaps ˜4 smaller inletlines and ˜4 smaller outlet lines (not shown). This may make for a lesscumbersome unit with smaller bend radiuses and may allow slightly moreevenly distributed coolant flow through the micro-channel cooler (notshown); however, the deep main inlet and outlet channels (not shown)within the UV LED lamp head module 200 essentially eliminate pressuregradients at the point of entrance to and exit from the preferablemicro-channel cooler channels (not shown). In one embodiment, coolantenters the UV LED lamp head module 200 via inlet cooling tube 203 atbetween 1-100 PSI and preferably between approximately 15-20 PSI at atemperature of between about 5-50 degrees Celsius (C) and preferably atabout 20 degrees C. and exits via outlet cooling tube 204 at atemperature of between about 10-100 degrees C. and preferably atapproximately 24 degrees C.

According to one embodiment, waste heat from various internal components(e.g., LED driver PCBs and LED array) of the UV curing system may bedissipated into the lamp body (not shown) and carried away by coolantflow to a heat exchanger and/or a chiller. An exemplary chiller isavailable from Whaley, USA. In one embodiment, the chiller utilizes ahighly efficient scroll compressor (available from Emmerson, USA).Depending upon the usage model, the chiller may be of the “split”variety in which the reservoir, pump, evaporator and controls arelocated inside a building housing the UV curing system, and the rest ofthe components, such as scroll compressor, fan, condenser, etc. arelocated outside the building (e.g., on the roof or on the side of thebuilding). It should be noted that many or all of the chiller or heatexchanger components may be operated in series or parallel or acombination of both for one or more UV LED lamp head modules 200 and/orsupply components. By way of example, one large chiller could beemployed for multiple UV curing systems that may have one or more pumpsand or reservoirs. An exemplary heat exchanger element for water to airis available from Lytron, USA. Any cooling solution could use a bypassarrangement so that differing pressure or flow rates could go throughthe evaporator and the micro-channel-cooler simultaneously.

According to one embodiment, the cooling liquid (coolant) compriseswater. The coolant may also contain one or more bio-fouling inhibitors,anti-fungicides, corrosion inhibitors, anti-freezing materials (e.g.,glycol) and/or nano particles (e.g., alumina, diamond, ceramic, metal(e.g., nano copper), polymer, or some combination) for enhanced heattransfer, and the coolant system could contain membrane contractors,oxygen getters and micron filters. Nano particles, such as titania,excited by UV lamp energy for the dual purpose of enhancing thermalconductivity and/or heat transfer and due to the resulting Photo-Fentonprocess the elimination of biological materials, such as funguses andthe like. Membrane contractors effectively reduce CO₂ in the water andhelp to maintain optimal pH for optimal corrosion resistance of coppermicro-channel surfaces.

In one embodiment, a sliding vane pump (available from Fluidotech,Italy) may be employed. It has a flow rate of greater than ˜4 GPM andpressure as high as ˜60 PSI. This flow rate is well-suited for themicro-channel cooler architecture described in connection with variousembodiments of the present invention (e.g., serial connection of 4 ormore 80 mm UV LED lamp head modules 200). The pump also is very quiet,compact, long lasting, and efficient, as it only consumes ˜0.25 KW. Invarious embodiments, redundant coolant pumps may be employed to reduceopportunities for a single point of failure. Average flow rate may beapproximately 0.75 GPM (range 0.1 to 10 GPM) per lamp head.

FIGS. 3A-B provide cut-away views of the UV LED lamp head module 200 ofFIG. 2A. From these views, it can be seen that an optical reflectorlayer 350 comprising reflector 201 is mounted to a body 305 enclosedwithin housing 202. According to one embodiment, body 305 is constructedfrom copper or a dielectric polymer material (e.g., PEEK; Torlon; LCP;acrylic; polycarbonate; PPS potentially filled with fillers, such asgraphite, ceramic, metals, carbon, carbon nanotubes, graphene,nano-sized or micron-sized flakes, tubes, fibers, etc.). Some of thesefilled resins are available from Cool Polymers of North Kingstown, R.I.The lamp body 305 may be machined with 5-axis milling or injectionmolded. Alternatively, body 305 may be injection molded and optionallysecondarily milled or drilled. As described further below, variouscomponents may be mounted directly or indirectly to the body 305,including, but not limited to, the housing 202, the reflector 201, anLED array 330, the micro-channel cooler (preferably forming part of thecommon anode substrate for the LED array 330), cathode claws 321 andanode bus body 315 a-b, and one or more LED driver printed circuitboards (PCBs) 310, which are preferably metal core PCBs (MCPCBs) and theanode bus body 315 a-b may serve as the metal core of the MCPCBs (a/k/acommon anode back plane).

In the present non-limiting example, body 305 has formed therein a maininlet lamp body lamp body cooling fluid channel 360 and a main outletlamp body cooling fluid channel 361 both of which run the length of body305. The main inlet lamp body cooling fluid channel 360 is in fluidcommunication with the inlet cooling tube 203 via a first coolant inlet(not shown) formed in the base of the body 305. The main outlet lampbody cooling fluid channel 361 is in fluid communication with the outletcooling tube 204 via a second coolant inlet (not shown) formed in thebase of the body 305. The channels 360 and 361 are sized such thatcoolant flows substantially uniformly through a micro-channel cooler(not shown) disposed there between. In one embodiment, the first andsecond coolant inlets may be on opposite ends of the base of the body305, across from each other, staggered, or some combination thereof tofacilitate equal and uniform flow of coolant from the main inlet lampbody cooling fluid channel 360 to the main outlet lamp body coolingfluid channel 361 through the micro-channel cooler. In alternativeembodiments, multiple inlet lamp body cooling fluid channels andmultiple outlet lamp body cooling fluid channels may be used.

In one embodiment, flow balance through the micro-channel cooler isachieved by designing the primary coolant inlet and exit manifoldchannels that run parallel to the longitudinal axis of the LED array 330to reach a level of pressure drop that is nearly homogeneous along theirlength by extending the channel depth to a point that the coolantpressure differential near the top of the channel (nearest themicro-channel cooler (not shown)) has reached a point of nearhomeostasis along the entire length of the channel by spreading out fromthe inlet port, or converging to the exit port by way of a very deepchannel. In other words, the exceedingly deep channels 360 and 361 givethe coolant sufficient time, hydraulic resistance and surface drag tospread out along the length of the micro-channel cooler and achieve asmall pressure differential near the top of each channel thereinresulting in balanced flow through each micro-channel under the LEDarray 330.

According to one embodiment, sub-assembly components of the LED driverPCBs 310, include, but are not limited to, LED driver controller ICs(not shown, which could also be part of a DC/DC converter system), FETs312, gates (not shown), inductors 311, capacitors (not shown), resistors(not shown) and cathode bus bars 304 a-b. As indicated above, in oneembodiment, the LED driver PCBs 310 are multi-layer metal foil (e.g.,copper)/dielectric layers on a metal (core) substrate (e.g., MCPCB)(available from Cofan, Canada) and are coupled (e.g., affixed viascrews) to the body 305 with an intervening thermal conduction compoundin order to dissipate the waste heat from the driver assemblies into thebody 305 where it is carried off by the coolant flow through the maininlet lamp body cooling fluid channel 360 and the main outlet lamp bodycooling fluid channel 361. In the present example, the channels 360 and361 extend deep enough in the body 305 to provide cooling to the areasubstantially under the FETs 312 and inductors 311, where a significantamount of waste heat is generated. Vias may be used to electricallyconnect the multi-layer metal foil layers.

In one embodiment, LED driver assembly PCBs 310 a-b, containing surfacemount electrical components and other semiconductor components are atleast 90% efficient. Exemplary high current capable and efficient LEDdriver ICs (not shown) are available from National Semiconductor USA(e.g., part LM 3434 or LM 3433 or a substantially equivalent). Linearand Maxim, USA also make similar parts. LED driver ICs (not shown) aresemiconductor junction p-n containing devices, preferably silicon based,that allow the buck conversion of a higher voltage/lower current inputto be converted to a lower voltage and higher current amenable to thehigh current LED driving conditions desired in various embodiments ofthe present invention. PWM may be employed.

Individual LEDs or groups of LEDs of the LED array 330 are driven bycorresponding segments of LED driver PCBs 310 a-b. For example, 4 groupsof 17 LEDs per side of the UV LED lamp head module 200 driven atapproximately 3 A (range 0.5 to 30 A) per LED and approximately 4.5-5V(range 2-10V). In such an embodiment, the LED array 330 comprises 68LEDs in 2 rows of LEDs (136 total), with opposite LED groupselectrically driven and/or controlled by corresponding LED driver ICs ataround 3 A per LED resulting in an approximately 2 kW input per UV LEDlamp head module 200. Another non-limiting example would be 16 LEDs in15 groups×2, which may be driven at approximately 4 V and 40 A per group(range 1-10 V and 1-500 A) and have an input of only approximately 12 Vinto the LED driver PCBs 310 a-b.

In some embodiments, due to the high efficiency of the surface mountelectrical components and other semiconductor components, custom metalcore PCBs (MCPCBs) can be constructed such that they may be affixed,preferably with screws or other means, to the sides of the body 305, andbe conduction cooled through the interface material and into thethermally conductive body 305. The waste heat ultimately being removedby the convective transport of the coolant flow through the body 305.For example, two LED driver PCBs 310 a-b, one on each side of the body305, may be constructed on a 2.5 mm (range 0.1-10 mm) thick copper coreboard that has approximately 4-12 mil thermally conductive dielectricmaterial layers (available from Thermagon USA and/or Cofan, Canada). Inone embodiment, highly thermally conductive dielectric layers areinterposed between copper metal layers (e.g., 1-4 oz copper foil layers)of the LED driver PCBs 310 a-b, which are affixed to body 305. Each LEDdriver PCB 310 a-b (e.g., ×2) may have 4 electrically isolated cathodicsegments corresponding to the locations of the 4 groups of LEDs isolatedby flex-circuit sections (4 of which are shown in the cut-away explodedview of FIG. 6—two of which are driven by opposing LED driver PCBs 310a-b). In one embodiment, the LED driver PCBs 310 a-b and theflex-circuit sections are arranged orthogonal to each other. Anothernon-limiting example is that each side of the body 305 has one LEDdriver PCB 310 a-b affixed to each side with 4 separate LED drivercontroller ICs located on each PCB (8 LED driver controller ICs total,that in sum can be driven up to around 2 kW or more per (e.g., 80 mmlong) UV LED lamp head module 200). Again, by affixing the LED driverPCBs 310 to the sides of the body 305, the waste heat from the LEDdriver PCBs 310 a-b may be dissipated into the body 305 and carried awayby the coolant flow to the heat exchanger or chiller. In one embodiment,a thermally conductive grease or other compound may be placed betweenthe LED driver PCBs 310 a-b and the body 305. In alternativeembodiments, the LED driver PCBs 310 a-b could be attached to the body305 in a non-thermally efficient manner and be convectively cooled viafans.

According to one embodiment, a common anode substrate layer 317 isclamped between cathode claws 320 a-d and 321 a-d and anode bus body 315a-b. A monolithic U-shaped common anode is formed by anode bus body 315a-b (which are substantially parallel to each other) and the commonanode substrate layer 317 (which is substantially orthogonal to theanode bus body 315 a-b). In another embodiment, the common anodesubstrate 317 and the anode bus body 315 a-b may form a monolithicrectangular or square shaped common anode.

In one embodiment, one surface of cathode claws 320 a-d and 321 a-d issubstantially parallel to the cathode portion of the common anodesubstrate 371 and another surface is substantially parallel to a topsurface of the LED driver PCBs 310 a-b, thereby allowing the to makeelectrical contact between these two layers. Further details regardingthe assembly forming the common anode substrate layer 317, includingmounting mechanisms for affixing the cathode claws 320 a-d 321 a-d, theanode bus body 315 a-b, are provided below.

In the present example, reflector 201 is a large (macro: e.g., ten's ofmillimeters in height), modular, non-imaging reflector structure havinga mid-portion 352 significantly wider than either entrance 351 or exitapertures 353. Such a structure is well suited to printing applicationswhere short stand-off distances (e.g., 2 mm) from the work piece to thereflector 201, and high irradiance (e.g., greater than ˜50 W/cm2) arebeneficial for high process speed, cure hardness and cure completeness(tack free).

In one embodiment, reflector 201 captures and controls approximately 90%or more (range 50-99%) of the light emitted by the LED array 330 andeach half of the elongate reflector 201 is an ellipse having a focalpoint on the opposite side of the centerline of the projected opticalpattern on the work piece, with the result of increasing the peakirradiance over a traditional shared focal point (along the projectedbeam centerline) design approach. Compound ellipses or other compoundparabolic shapes may also be considered. In one embodiment, reflector201 is designed to have a high angular extent of approximately 80degrees (range of 45-90 degrees).

Embodiments of the present invention seek to produce a high-quality cure(e.g., 100% or nearly so) by producing both high peak irradiance andhigh total output power (e.g., approximately 184 W per UV LED lamp headmodule 200) as photo-initiators can be toxic (and expensive) and uncuredinks, coatings, or adhesives are undesirable. As noted above, highirradiance results in faster, deeper, and harder cured materials.Consequently, embodiments of the present invention, seek to achieve peakirradiance levels that are approximately ten times (or more) the levelsdisclosed in current state-of-the-art UV LED (and mercury lamp) curingsystems while also maintaining both high efficiency and long life of theLEDs.

According to one embodiment, reflector 201 is easily factory swappableand preferably field-replaceable thereby allowing other reflectors to beattached to the body 305 of UV LED lamp head module 200 for differentapplications, which might fulfill different process goals/parameters. Inthe present example, reflector 201 is shown as an elliptical reflectorthat is of two-part construction, where the two major components are theopposing sides of one or more ellipses. Reflector 201 may be machined ona five-axis mill and then polished with a diamond grit polish or it maybe extruded metal and post polished, or it may be extruded polymerwithout the need for post polishing due to the prior polishing of themold cavity/extrusion die. As described above, reflector 201 may be ofmodular design, such that an application, such as ink curing on a flatsubstrate that demands a narrow projected focal beam “line” of highirradiance (output power density) could use a bolt on ultra-highintensity line generating reflector (not shown), whereas an applicationon a rough topological substrate that demands a longer depth of fieldcould require a reflector pair (not shown) specifically designed forthis longer depth of field (or longer depth of focus) that is easilyinterchanged with the high intensity reflector pair by simply unboltingthe previous reflector pair and bolting the new reflector pair in placeas described in more detail below. Similarly, a reflector pair may bespecifically configured for long working distance with high intensity orlong working distance with a wide area smooth intensity beam pattern onthe work piece. Locating pins between the reflector 201 and the commonanode substrate layer 317 may be employed.

In one embodiment, the internal surface of the preferably injectedmolded polymeric reflector 201 is a silver vacuum-deposited coating withan ALD (atomic layer deposition) protective overcoat that is corrosionresistant due to the pin-hole free nature of the ALD process. The silvercoating may be deposited using various deposition processes (e.g., ALD,CVD, sputtering, evaporation, sol-gel). As polycarbonate is aninexpensive polymeric reflector resin, a vapor barrier should be placedon the polycarbonate before the silver is deposited so that the side ofthe silver coating facing the polymeric reflector substrate does notallow corrosive vapor (molecules) to corrode the silver from the insideout. Low vapor permeable resins (e.g., E48R (Zeon Chemicals, USA)) maybe considered. Also, vapor barriers (e.g., copper, ALD oxide coatings)may additionally be considered and, deposited on the reflector prior tothe silver or aluminum coating. The ALD dielectric overcoat is selectedfrom the group of oxides (e.g., Al₂O₃) or fluorides (e.g., MgF₂) or somecombination thereof. Alternatively, an HR coating on the reflector 201can also be a dielectric overcoated aluminum coating on an injectionmolded polymeric reflector. The dielectric coating is preferably asingle layer magnesium fluoride or silicon dioxide tuned for peakreflectivity around the wavelength that is best suited to theapplication. A dielectric stack based on optical interference may beemployed for any of the above-mentioned configurations to increase peakirradiance in the selected wavelength range.

Embodiments of the present invention may employ secondary optics (notshown) for beam control and/or a window (e.g., a lens) 340 that has anantireflective (AR) coating. The AR coating is preferably a BAAR (broadangle antireflective) coating as the angles emitting from the exitaperture 353 may be in excess of 45 degrees, as such high angles wouldundergo significant deleterious reflection from the window surface ifsuch a BAAR coating was not used. High UV resistant acrylic for tanningbeds could be considered, but borosilicate glass is preferable forwindow 340 and secondary optics. In one embodiment, a window mount 341holds window 340 in place as described further below. According to oneembodiment, an o-ring (not shown) is situated between the window 340 andreflector 201. In one embodiment, the external housing for the reflector201 may be injection molded. In various embodiments, an inert gas ormicro-porous spheres (available from Zeolite, USA) may be used tocontrol water vapor. This vapor can be an issue for LED longevity shouldno encapsulant over the LEDs be employed. Current state-of-the-art doesnot allow for an LED encapsulant (such as high purity silicone) to beemployed as yellowing from the high photon energies of the short UVwavelengths is an issue. Silicone encapsulants from Schott (Germany)with low carbon content are known to be the least yellowing in existenceat this time.

For purposes of measuring a distance from the window 340 to a work piecesurface, it is to be understood that the window 340 has an inner surface(closest to the surface of the LED array 330) and an outer surface(closest to the surface of the work piece). Herein, distances to thework piece are generally measured with respect to the outer surface ofthe window 340.

FIG. 3C is a top-level isometric exploded view of the UV LED lamp headmodule 200 of FIG. 2A. According to the present example, electricalpower is provided to the UV LED lamp head module 200 via a cathode cable205 and an anode cable 206, which are in turn coupled to cathode crossplate 375 and anode cross plate 376, respectively. In the presentexample, the cross plates 375 and 376 both include tubular structuresorthogonal to their top surfaces to accept the corresponding cables 205and 206 via preferably solder connections. The cathode cross plate 375is wider than the anode cross plate 376 to provide an electricalconnection with the cathode bus bars 304 a-b, which in turn is coupledto the front surface of the LED driver PCBs 310 a-b, which are generallycathodic layers separated by dielectrics and ultimately separated fromthe anodic common anode body (the metal core of the MCPCB) by one ofthese dielectrics layers. The anode cross plate 376 engages with themetal core (common anodic backplane) of the LED driver PCBs 310 a-b. Inone embodiment, it may be preferable to have the primary anode cable 206and primary cathode cable 205 located at opposite ends of the lamp base305 for enhanced current spreading purposes.

Now, moving from the electrical input and coolant input end of the UVLED lamp head module 200 to the light emitting end of the UV LED lamphead module 200, cathode claws 320 a-d and 321 a-d may serve severalfunctions, including (i) carrying the electric current from the cathodeside of the LED driver PCBs 310 a-b to the cathode layer encompassed inthe flex-circuit assembly bonded to the replaceable monolithicmicro-channel cooler assembly (e.g., part of LED package 318); (ii)clamping the LED package 318 to the lamp body 305; and (iii) clampingthe LED package 318 to the anode body 315 a-b. In one embodiment, thecathode claws 320 a-d and 321 a-d clamp down on to the cathode side ofthe LED driver PCBs 310 a-b thereby forming a complete cathodicelectrical path for low impedance current flow with low electricalcontact resistance. The cathode claws 320 a-d and 321 a-d may be slottedto allow clamping action via vertical (along the optical output axis)screws 319 to pull down and compress the separator gasket (o-ring) 314and force a common anode substrate layer of LED package 318 in contactwith the anode bus body 315 a-b thereby forming a complete anodicelectrical path for low impedance current flow with low electricalcontact resistance.

Depending upon the particular implementation, cathode claws 320 a-d and321 a-d could be replaced with alternative cathode connectors/bodies ofvarious forms, including, but not limited to, bent metal foil, stampedspring foil, metal molded 3 dimensional geometries, flex-circuit andeven wire.

In one embodiment, the micro-channel cooler assembly is clamped to theanode bus body 315 a-b and/or the lamp body 305 with screws providingthe clamping force. By unscrewing the potentially polymeric screws thateffectively may clamp and sandwich the aforementioned LED package 318between the anode and cathode assemblies, the LED package 381 orportions thereof, e.g., the micro-channel cooler assembly, can be easilyremoved and replaced.

The micro-channel cooler may be plated with the ENEPIG or ENIG processavailable from Superior Plating USA prior to the flex-circuit beingoptionally bonded to it, or after the flex-circuit is optionally bonded,or just the flex-circuit may be plated. The advantage to the ENEPIGprocess is that it is a universal coating in that lead-free soldercomponents may be bonded to it as well as gold wires used in the wirebonding of the LED cathodes to the flex-circuit cathodes. Other coatingsmay be considered. It should be noted that it is preferable that onlythe areas of the entire apparatus (other than the LED bond pads) thathave a gold containing layer be found on the top conductive materiallayer of the flex-circuit found at the opposite end of the wires thatrun to the LED bond pads. In some embodiments, the micro-channel coolerassembly and the anode body 315 a-b may have clearance holes for cathodewires to travel through, and the cathode wires may then be soldered orset screwed in place in the cathode bus bars 304 a-b. It is desirable touse large core, high strand count, small gage wire that has minimalsheathing thickness so the clearance holes do not have to be undulylarge and thereby making the overall assembly unduly large. A goodcompromise between low voltage drop and small size is 10, range 1-30,Gage wire with 105 strands available from Alpha Wire and or CableCo USA.The anode and cathode parts may be plated for low contact resistance.Also, a petroleum based gel could be used if bare copper is chosen forany contact surface.

In the current example, anode cross plate 376 is affixed to the anodebus body 315 a-b via preferably metallic screws that are inserted intothreaded holes in the edge of the anode bus body 315 a-b. Alternatively,if one were not concerned with ease of replaceability and/or disassemblysuch contacts could be soldered. This alternative could be considered inthe context of other mounting mechanisms described herein, such as thecathode claws' 320 a-b and 321 a-b interface with either the LED driverPCBs 310 a-b or the cathode layer of the flex-circuit (not shown).Similarly, cathode cross plate 375 is shown as being affixed (e.g., withmetallic screws) to the cathode bus bars 304 a-b, which extend slightlybeyond the edge of the anode bus body 315 a and 315 b, respectively, toprovide an air gap between the anode bus body 315 a-b and the cathodecross plate 375 to prevent electrical shorting.

In one embodiment, an air gap (not shown) is provided between the crossplates 375 and 376 lamp body 305 for several reasons. Firstly, in oneembodiment, anode bus body 315 a and 315 b, common anode substrate layerof LED package 381, a cathode layer of the flex-circuit (not shown) andcathode claws 320 a-d and 321 a-d serve in a synergistic fashion to makethe various electrical contacts (anode-to-anode and cathode-to-cathode)through a clamping or pinching function. Consequently, if the crossplates 375 and 376 did come into contact with lamp body 305 they couldunload the inherent preload function of cathode claws 320 a-d and 321a-d. Secondly, it is preferable that lamp body 305 be thermallyconductive and thermally conductive materials are sometimes alsoelectrically conductive (e.g., electrically conductive graphite fillerin a polymeric resin, such as polycarbonate or PPS or base metallicmaterials, such as copper, stainless steel or aluminum). As such, theair gap between the cross plates 375 and 376 serves to prevent shortingin such embodiments. In alternative embodiments, the lamp body 305 maybe thermally conductive and electrically insulating, such as D5506liquid crystalline polymer (LCP) a filled electrically insulatingpolymer available from Cool Polymers, USA.

Alternatively, the cross plates 375 and 376 could be attached or affixedto the lamp body 305 with polymeric screws for stress relief purposes.Additionally, glue means and the use of shims can be considered for easeof assembly and to account for dimensional tolerance stack up inproduction can be considered.

It should be noted that one should be cognizant of the fact that lampbody 305 (if it is in fact electrically conductive) is in contact withthe common anode substrate layer 317. As such, electro-chemical (e.g.,galvanic) corrosion can be encountered if dissimilar electro potentialscome in direct contact or even in close proximity or even in indirectcontact via fluid flow, for example. Therefore, materials used forcommon anode substrate layer 317 and materials used to facilitatethermal conductivity of lamp body 305 should be selected with care. Inone embodiment, a copper anode substrate layer 317 is paired with agraphite filler of lamp body 305. If body 305 was aluminum and the anodesubstrate layer 317 was copper this would pose an enormous corrosionproblem, for example.

With respect to lamp body 305, it is noted that due to the high aspectratio and deep, narrow main lamp body cooling fluid channels 360 and361, injection molding may be the most practical means of manufacturing;however, drafting of the external surfaces of the lamp body 305 wouldinterfere with the orthogonal nature of the electrical contact pointswhere the anode bus body 315 a and 315 b contacts common anode substratelayer 317 at preferably a zero or ninety degree angle in order toprovide for low electrical contact resistance (i.e., two orthogonalsmooth surfaces (plate-to-plate contact) vs. two surfaces meeting at anangle (sharp edge-to-plate contact)).

According to one embodiment, using a mold within a mold technique(wherein each half of the inner mold has a modular hand-load side), aninner mold is used to define the outer envelope and/or features of lampbody 305. When the two halves are pulled apart, the lamp body 305 isejected without the need for draft thereby enabling the desired flushand parallel and/or orthogonal mounting of anode bus body 315 a-b,common anode substrate layer 317 and cathode claws 320 a-d and 321 a-ddue to the lack of drafting angle. The need for draft is eliminated as aresult of the two-part construction, which reduces the surface area by50% and doubles the rigidity of the mold allowing for the two moldhalves to be pried part and the lamp body to be ejected despite the factthe fact that no draft is in the mold because there is, among otherfactors, a 50% reduction in surface drag during the ejection as comparedto a traditional single piece mold. With the thermally conductivepolymers contemplated, their high thermal conductivity require a highermold surface temperature than would traditionally be utilized (so theresin doesn't “freeze” in the mold). Furthermore, because no fillerparticles can be sloughed out into the coolant during UV LED lamp headmodule operation as the micro-channel cooler could potentially becomeclogged, even higher mold surface temperatures are preferable to createa resin-rich “skin” that will fully contain the filler particles withinthe resin matrix.

Another potential issue with using a traditional injection moldingprocess is the deep and narrow and high aspect ratio main inlet andoutlet lamp body cooling fluid channels 360 and 361 may lead to abending of the thin parallel plates of the mold used to define the maininlet and outlet lamp body cooling fluid channels 360 and 361. Thisissue is uniquely addressed, in one embodiment, by using a verticalinjection molding process, involving balanced multipoint injection flowand pressure so as to not bend (deform) the metallic plates that form(define) the channels.

According to one embodiment, a two-part strain relief clamp 306 is usedto remove stress from cathode cable 205, anode cable 206, cathode crossplate 375 and anode cross plate 376 as strain on these components wouldotherwise be transferred to the fragile LED driver PCBs 310 a-b.

Returning briefly to the cathode claws 320 a-d and 321 a-d, in oneembodiment, a beryllium copper or other conductive metal corrugatedstrip could be placed between the cathode claws 320 a-d and 321 a-d anda top surface of an electrically isolated cathodic foil of amicro-channel cooler assembly of LED package 318 for the purpose ofproviding a spring type action between these components. This couldeffectively negate the need for the preferably 0-80 screws that clampthe cathode claws 320 a-d and 321 a-d to the foil. Instead, theorthogonal screws through the cathode claws 320 a-d and LED driver PCBs310 a-b and into the lamp body 305 could clamp the cathode claws 320 a-dand 321 a-d in place if a downward force was temporarily supplied toforce the spring flat or nearly so, thus providing a low electricalresistance connection with one less screw. This same or substantiallysimilar concept could be employed on the anode edge of the anode busbody 315 a-b nearest the backside of the lamp body 305, however, one mayconsider a substantially monolithic corrugated beryllium copper or otherelectrically conductive material. An anode tie bar could wrap around thePCB and have orthogonal slots to accept screws. Solder or conductiveadhesive can always be considered but they would affect ease ofrepairability. It should be noted that by affixing or clamping the LEDdriver PCBs 310 a-b to the sides of the lamp body 305 this preferablymates the components in excellent thermal communication thereby allowingthe flowing coolant to cool the LED driver PCBs 310 a-b as, in oneembodiment, they have waste heat dissipation requirements of around0.5-1 W/cm²+/−. Ultra high efficiency switching electronic SMDcomponents of greater than 90% efficiency are preferable. In oneembodiment, the deep high aspect ratio coolant channels 360 and 361synergistically add surface area to lower the heat transfer coefficientrequired to cool the LED driver PCBs 310 a-b while at the same timeadding sufficient hydraulic resistance to balance the flow through themicro-channel cooler 410. The thin walls of the lamp body 305 not onlylower the thermal resistance between the LED driver PCBs 310 a-b and thecoolant flow, but also allow for the cathode foil layer 513 of theflex-circuit 510 to be shorter in length (measured from the end of themicro-channel cooler 410 to the edge near the wire bonds).

Additionally, Lineage USA will have platinum rated conduction cooled1000 W power supplies commercially available in 2011. These powersupplies are 95% efficient, and in principle will not need any coolantwater to carry away the waste heat, and just natural convection is used.It should be finally noted that if ˜1100 W ˜12V Power-One front endAC/DC power supplies were used, one could use two of the units per ˜80mm UV LED lamp head module containing about ˜136 LED (of, for example,SemiLEDs' ˜1.07×1.07 mm LEDs).

According to embodiments of the present invention, it is preferable tonot solder LED package 318 or the micro-cooler assembly to the LEDdriver PCBs 310 a-b as this method would decrease modularity andincrease integration, with the net result of decreased repairability orreplacement of sub-components. As an example only, if one of the LEDdriver PCBs 310 a-b fail, it may simply be unscrewed using preferablyinjection molded, or machined polymer (nylon, PEEK, Torlon) screws, aspreviously described, and replaced with a repaired or new board. Thesame holds true for LED package 318 preferably directly bonded to amicro-cooler assembly as described further below.

In relation to assembly of various components of the UV LED lamp headmodule 200, in a preferred but non-limiting example, 0-80 tapped holesmay be placed in the edges of the LED driver PCBs 310 a-b that face thedirection of light output (which is to say facing the anode side of themicro-cooler assembly). Secondly, small claw-shaped cathode claws 320a-d and 321 a-d that are preferably of copper or aluminum construction(and machined, molded, or stamped) and in the aggregate being of thesame approximate dimension in the long-axis of the LED array direction(individually, the same approximate length of the isolated LED driverPCB 310 a-b and/or flex-circuit segments). When the LED driver PCBs 310a-b are pushed up tight (as sliding is allowed by slots in the LEDdriver PCBs 310 a-b when they are lightly screwed to the lamp body 305)to the anode over-hanging side of the micro-channel cooler, and thenscrewed in place with separate screws to the sides of the lamp body 305,the cathode claws 320 a-b and 321 a-b are placed on the protrudingcathodic flex-circuit sections, and the orthogonal surfaces of thecathode claws 320 a-b and 321 a-b are placed over their respectivepositions on cathode pads of the LED driver PCBs 310 a-b. Then, 0-80polymer screws (or metal screws with non-conductive polymeric sleevesand/or washers) are placed through the cathode claws 320 a-d and 321a-d, through LED package 318 (e.g., including micro-channelcooler/flex-circuit assembly) and into threaded holes in the (top lightemitting direction of the lamp body 305) and tightened using a pre-settorque production screwdriver unit. Any embodiment could use metalscrews with non-conductive polymeric sleeves and/or washers or polymerscrews. For the same reason, non-conductive screws or polymeric sleevesand/or washers might be employed, the cathode layer 513 of flex-circuit510 might be pulled back to avoid contact with metal screws to avoidelectrical shorting of any layers. Metal screws could be in contact withand carry electrical current between anode and/or cathode layers.

If used, the polymer screws (which could be machined or molded atCraftech USA) are then firmly tightened which then complete the functionof making a very low electrical resistance contact between anodicsurfaces of the micro-channel cooler and LED driver PCBs 310 a-b, andthe proper cathodic surface locations of the flex-circuit cathodicsegments and the cathode claws 320 a-d and 321 a-d and the pads on theLED driver PCBs 310 a-b. It should be noted that most or all of thescrewing and/or affixing operations mentioned above could beaccomplished with preferably low melting temperature solder or glue orother affixing means; however, for purposes of ease of repairabilityscrews are described as the affixing means in the context of variousembodiments of the present invention. It is also contemplated that aslot could be placed in LED driver PCBs 310 a-b such that each side ofthe slot accepts the protruding portions of the micro-channelcooler/flex circuit. The protruding portions of the flex-circuit couldthen be inserted into these slots and preferably soldered in place afterthe LED driver PCBs 310 a-b are preferably screwed to the side of thelamp body 305. It should also be noted that spring contacts made from anelectrically conductive material such as beryllium copper, which couldbe used preferably in place of the aforementioned adjustable cathodeclaws.

FIGS. 4A-B provide magnified cut-away views of a bottom portion ofreflector 201 and a top portion of body 305 of the UV LED lamp headmodule 200 of FIG. 2A. In these views, LED array 330 and various aspectsof the common anode substrate layer 317 become apparent. Additionally,in these views, separator gasket 314 is depicted as being formed of aplurality of o-rings 420 and a preferred multilayer construction of theLED driver PCBs 310 a-b becomes visible.

As described in further detail below, in one embodiment, a micro-channelcooler 410 provides the common anode substrate layer 317. According toone embodiment, micro-channel cooler 410 is a diffusion bonded etchedfoil micro-channel cooler including a heat spreader layer (not shown)diffusion bonded to foil layers (not shown) having etched thereinvarious primary inlet/outlet micro-channels 411 and internalmicro-channels (not shown). While micro-channel cooling does have alaminar component in which the boundary layer is compressed, inembodiments of the present invention, impingement cooling (e.g.,turbulence) may result from etched coolant flow path shape and/ordirectional changes. An exemplary micro-channel cooler is illustrated byU.S. Pat. No. 7,836,940, which is hereby incorporated by reference inits entirety for all purposes. Micro-channel coolers meeting the coolingrequirements described herein are available from Micro-Cooling Concepts,USA. Those skilled in the art will recognize that various other coolingschemes may be employed. For example, macro-channel cooling and otherturbulent flow cooling paths (e.g., impingement, jet-impingement) ortwo-phase/nucleate boiling (or some combination), and cooling schemesmay be considered.

According to various embodiments of the present invention, one objectiveis to create and maintain a relatively isothermal state (e.g., junctiontemperatures within approximately ±1 degree C. and also generally amaximum average junction temperature of ˜40 degrees C. (range 30-200degrees C.) from end-to-end of the LED array 330. To achieve thisobjective, embodiments of the present invention attempt to balancecoolant flow through the micro-channel cooler 410 from front to back,top to bottom, end to end and/or side to side. In alternativeembodiments, the flow may be balanced or imbalanced to accommodatedesign needs. The coolant may flow through internal primary andsecondary channels (not shown) of the micro-channel cooler 410 invirtually any direction, selected from vertical, horizontal, orthogonal,parallel, etc., or any combination thereof, with respect to the bottomsurface of, as well as under, the LEDs of the LED array 330. Another wayof describing the orientation of the channels is with respect to the p-njunction plane, which is (in most LEDs) substantially parallel to thebottom surface of the LED.

Similarly, the internal primary and/or secondary channels they may beinterconnected with virtually any orientation of manifold(s) selectedfrom vertical, horizontal, orthogonal, parallel, diagonal, angular,by-pass, partial by-pass, etc., or any combination thereof, again withrespect to the orientation of the bottoms of the LEDs (or the p-njunctions of the LEDs). It is preferable that all, or almost all (near100%) of the coolant eventually flows from the top portion (e.g., maininlet micro-channel cooler cooling fluid channel 430 b) of main inletlamp body cooling fluid channel 360 through the micro-channel cooler 410to the top portion (e.g., main outlet micro-channel cooler cooling fluidchannel 430 a) of main outlet lamp body cooling fluid channel 361 in adirection that is orthogonal, or perpendicular, to the long-axis of theLED array 330 and/or micro-channel cooler 410. In one embodiment,micro-channel cooler 410 utilizes flow paths optimized by CFD to reduceflow velocities to such a level so as to greatly reduce erosion. In oneembodiment, coolant velocities of approximately 2 meters/sec. arepreferred to reduce erosion of the channels. Ceramic materials may beused for the channel substrate to even further eliminate erosionpotential.

As noted earlier, the main inlet lamp body cooling fluid channel 360 andthe main outlet lamp body cooling fluid channel 316 are sized such thatthe coolant flows uniformly through the etched foil internalmicro-channels, and so that preferably nearly all of the coolanteventually ends up running in a substantially perpendicular direction tothe long axis of LED array 330, in that any given molecule of coolantthat starts in main inlet lamp body cooling fluid channel 360 eventuallyends up in the main outlet lamp body cooling fluid channel 361, and so,essentially each molecule of coolant eventually flows substantiallyperpendicular to the long-axis of LED array 330 (substantially parallelto the short-axis of the LED array 330) as it traverses micro-channelcooler 410 and flows under the LEDs. By making the main inlet lamp bodycooling fluid channel 360 very narrow (e.g., approximately 1-4 mm andpreferably approximately 2.3 mm) wide and very deep (e.g., approximately1-10,000 mm and preferably about 100 mm), the resultant hydraulicresistance aids in uniform micro-channel flow in terms of balanced flowthrough substantially all or most of the internal channels ofmicro-channel cooler 410, whether or not they be primary, cross,secondary, manifold, etc. channels. It should be understood that thesechannels could have curves, s-bends, protrusion for turbulence, andperhaps narrow and widen and/or deepen as they traverse the space underLED array 330 in the direction that is substantially lateral or parallelto the short axis of LED array 330. Again, the orientation of any givenmicro-channel can be in any orientation (as well as flow direction) withrespect to the orientation of the p-n junctions of the LEDs.

As described in further detail below, LED array 330, comprising lightemitting devices, such as LEDs or laser diodes, are mounted to themicro-channel cooler 410. In one embodiment, the range of the number ofLEDs along the length of the micro-channel cooler is 2-10,000, and thesize of each LED is approximately 1.07, 1.2, 2, 4 mm square (or 2×4 mm),range of 0.1-100 mm. The aspect ratio of the width to length ispreferably about 1:68 to 1:200, but the range may be 1:10-1:1,000. Itshould be noted that the LED arrays may not be high aspect ratio and maybe substantially square, substantially rectangular, substantiallycircular or other geometries. Exemplary LEDs are available fromSemiLEDs, USA. SemiLEDs' LEDs have a unique (often plated) coppersubstrate which is advantageously bonded to the copper (or ceramic)micro-channel cooler 410, thereby maintaining the thermal and costadvantageous of this high thermal conductivity material. According toone embodiment, the size of the LEDs employed are 1.07×1.07 mm squareand the LED array 330 comprises an array of 68 LEDs long by 2 LEDs wide.

In one embodiment of the present invention, the LEDs of LED array 330are placed substantially in electrical parallel, or have at least twoLEDs in parallel, on a preferably common anode substrate. This is a verythermally efficient manner of connection, as no thermally impedingdielectric layer between the base of the LED and the substrate need beadded for the purpose of electrical isolation as is needed in a seriesconfiguration or series/parallel configuration. Nonetheless, it shouldbe noted that any of these configurations could be considered in variousembodiments, as well as a purely series arrangement, or aseries/parallel arrangement. While a dielectric layer couldsubstantially add to overall thermal resistance, thereby raising thejunction temperature of the device(s) and adversely impacting outputpower and/or efficiency, it is contemplated that a very thin dielectriclayer on the order of a few microns thick or less may be grown by meanssuch as atomic layer deposition and provide a very low thermal impedancelayer over a material such as copper for the purpose of electricalinsulation in a series/parallel type arrangement. This dielectric couldbe selected from the group of oxides, nitrides, carbides, ceramics,diamond, polymers (ALD polyimide), DLC, etc.

According to various embodiments of the present invention, one objectiveis to maintain extremely low thermal resistance between the epitaxialp-n junctions of the LEDs, or at least the bottom of the preferably baredie, that is approximately 0.015 K-cm2/W, but the range may be 0.0010-15K-cm²/W, and is often around 0.024 K-cm²/W. Very thin layers of foil,bond pads, traces, etc. of either metallic, dielectric, ceramic, orpolymer layers may be considered, but are not optimal due to theincrease in thermal resistance that results from these additionallayers, which inevitably results in an increase in junctiontemperatures, with a corresponding decrease in efficiency. Various meansfor decreasing current droop associated with the epitaxial structuregrowth and design, such as thicker n or p capping layers may beemployed, as well as other state-of-the-art means (e.g., new quantumbarrier designs, reducing non-radiative recombination centers, etc.)found in recently published scientific journals, and authored byemployees of Philips, Netherlands, and RPI, USA, and others (see, e.g.,Rensselaer Magazine, “New LED Drops the ‘Droop’” March 2009 and CompoundSemiconductor Magazine, “LED Droop: Do Defects Play A Major Role?” Jul.14, 2010, both of which are hereby incorporated by reference in theirentirety for all purposes).

As such, in accordance with various embodiments, an extremely lowthermal resistance path exists between the LED junction and the etched(e.g., chemically etched) foil layers that contain flowing liquid in thepreferably chemically etched micro-channels, because the LEDs aredirectly mounted (preferably with 2.5 um thick SnCu solder), and theheat spreader (if employed) and foil layers are thin, and theypreferably do not enlist an intervening dielectric layer. Other etchingor lithographic or machining processes may also be considered in themanufacture of the micro-channels.

According to one embodiment, the LEDs of LED array 330 are bondeddirectly (i.e., no substantial intervening layer (whether bulk material,foil, thin-film, or other material) between the LED and themicro-channel cooler 410 other than, for example, a thin pre-sputteredsolder layer that is preferably pre-applied (e.g., by sputter depositionmeans) to a bottom surface of the LEDs.

As described in further detail below, a separator gasket 314 may beformed by one or more o-rings 420 to seal the common anode substratelayer 317 to the body 305 and also prevent coolant bypass substantiallydirectly under the LED array 330. While in this and other figures, theo-rings 420 a-c do not appear to be compressed, it will be appreciatedthat in real-world operation, they would in fact be compressed toperform their intended function of preventing fluid by-pass betweenchannels or into the external environment. In the present example,separator gasket 314 is substantially parallel to, and in the samez-axis plane, as the bottom surface (opposite to the light emittingdirection) of the diffusion bonded foil layers (not shown) of themicro-channel cooler (whether layered vertically or horizontally). Thecross-section of the separator gasket 314 is preferably substantiallyround, may be made of a soft durometer silicone, and may be manufacturedby Apple Rubber USA. In alternative embodiments, the cross-section ofthe separator gasket 314 may be square or rectangular.

With reference to the multilayer construction of the LED driver PCBs 310a-b illustrated in the present example, in one embodiment, copper (oraluminum, polymer, filled polymer, etc.) metal core PCB boards that areapproximately 2.5 mm thick (range 0.1-10 mm) and available from CofanCanada are constructed of multiple layers to keep the size of the PCB ata minimum. The high power FETs and gate drivers and inductors andresistors and capacitors may be mounted on the preferably Thermagon USAlayer that is closest to the metal core. In fact, in some embodiments,this layer could be windowed or cored so that the FETs (or other driverPCB components) can be mounted directly to the metal core with orwithout attachment screws. The LM 3434 or LM 3433 (examples only) seriesLED common anode drivers available from National Semiconductor USA couldalso be mounted as close as possible to the metal core as well, meaningthat a minimal dielectric layer thickness (if any) may exists betweenthe components and metal core. Equal trace path lengths and closecomponent spacing should also be considered for efficient electrical andstable operation. Custom wound inductors can increase drive sub-assemblyefficiency greatly. The inductors could be oriented in such a manner asto make the magnetic fields of the separate drivers (e.g., 8 or 15) witha preferable common backplane (e.g., anode body 315 a-b) that also maybe shared with the common anode substrate 317 of the micro-coolerflex-circuit assembly advantageously interacting with each other toincrease the efficiency of the preferably constant current driver(though a constant voltage driver may be considered, especially withspecial circuitry). Pulse width modulation (PWM) constant currentdrivers may be considered, although, PWM can have a deleterious effecton LED lifetime at high currents due to current ripple, additionalcapacitors between the inductors and the LEDs should be considered.Alternatively, an iron substrate could be placed between the inductorsto reduce undesirable interaction between the inductors or othercomponents that may be orientation and spacing dependent. Mostpreferably, shielded, off-the-shelf (OFS) inductors from VASHAY, Indiacan be considered.

On the backside of the lamp body 306 (the side where the main inputwater and electrical energy in/out sources are located) the preferablymetal (copper, aluminum, composite) MCPCB cores can have a screwed orsoldered tie bar (or anode cross plate 376) between the two MCPCB (PCB'swith metal cores available from Cofan, Canada) cores to make a spaceand/or strong mounting plate for a single wire connection for the anodethat will then run to the main AC/DC front end power supplies that areconnected to the AC mains.

In one embodiment, the metal cores of the LED driver PCBs 310 a-b arethe ground plains—there may be more than one ground plane on each LEDdriver PCB 310 a-b. As such, the edge of the PCB is preferably clampedor soldered to the ground plain of the common anode substrate layer 317.This is preferably accomplished by allowing the common anode substratelayer 317 to extend, or hang over, each side of the body 305, such thatthe anodic side of the common anode substrate layer 317 can touch and bein electrical communication with the anode side (edge) of the LED driverPCBs 310 a-b, and the cathodic sides of the common anode substrate layer317 (e.g., the top foil layer) can preferably touch and be in electricalcommunication with the proper top cathode area of the individualcathodic segments that are in electrical communication with the LEDdriver PCBs 310 a-b.

FIGS. 5A-B provide further magnified views illustrating LED array 330and its interface with common anode substrate 317 of the UV LED lamphead module 200 of FIG. 2. In these views, the high fill-factor of theLED array 330, the electrical coupling of the individual LEDs, theproximity of the base of the reflector 201 to the surface of the LEDsand the various layers of a flex-circuit 510 become apparent.Additionally, in these views, the preferably vertically-oriented foillayers of the micro-channel cooler 410 become visible.

According to one embodiment, common anode substrate layer 317 mayinclude a micro-channel cooler 410 for transferring heat from LED array330, an integrated etched capping layer 525 and a solid capping layer530. In one embodiment, the width of the micro-channel cooler 410 isonly slightly (e.g., less than about 400 microns (range 50-2,000microns)) wider than the LED array 330. In one embodiment, the totalwidth of the micro-channel cooler 410 is about 1.2 times (range 1, 1.1,1.3, 1.4, 1.5, 1.6, 1.7, 1.9, 2, 2.1, 2.2, 2.3, 2.4 to 2.5×) the totalwidth of the LED array 330. In the present context, computer modelingsuggests that increasing the total width of the micro-channel cooler 410to a width of nearly double (2×) the width of the LED array 330decreases the peak thermal resistance by only about 5%.

The micro-channel cooler 410 may include a heat spreader layer 540(a/k/a thermal diffusion layer) (e.g., approximately 125 microns thick(ranging from less than 500 microns, less than 250 microns, less than200 microns, less than 150 microns, less than 100 microns, less than 50microns, to less than 25 microns), below a top surface of themicro-channel cooler 410, a plurality of primary inlet/outletmicro-channels (e.g., primary inlet micro-channel 411) and various inletmanifold passages, heat transfer passages and outlet manifold passages.Notably, in the present context, the heat spreader layer 540 reallyprovides little true heat spreading; however, it does provide anextremely short thermal diffusion length (distance between the bottom ofthe LEDs and the closest of the heat transfer channels (not shown) ofthe micro-channel cooler 410). Exemplary heat transfer channels, theirorientation, flow directions and dimensions are provided by U.S. Pat.No. 7,836,940, incorporated by reference herein.

The top surface of the micro-channel cooler 410 may couple themicro-channel cooler 410 with LED array 330. Primary inletmicro-channels (not shown) may be configured to receive and direct afluid into internal passages within the micro-channel cooler 410,including heat transfer passages. The heat transfer passages may beconfigured to receive and direct the fluid in a direction substantiallyparallel to the top surface and substantially perpendicular variousinput and output manifold passages. The outlet manifold passages may beconfigured to receive and direct the fluid to one or more primary outletmicro-channels (e.g., primary outlet micro-channel 411).

In one embodiment, micro-channel cooler 410 may be formed from aplurality of etched foil sheets (e.g., foil sheet 520) having formedtherein the internal passages and manifolds for directing coolant flow.In the current example, a monolithic micro-channel cooler body is formedby diffusion bonding the combined etched capping layer 525 and solidcapping layer 530 to micro-channel cooler 410. As shown in FIG. 5A, foillayers of the etched capping layer 525 are preferably thicker than thefoil layers 520 of the micro-channel cooler 410. In one embodiment, thecapping layers 525 and 530 could be machined.

In an embodiment in which the diffusion bonded foil layers (e.g., foillayer 520) are vertically stacked (and diffusion bonded together) withtheir edges lying under the bottom portion of the LEDs as illustrated inFIGS. 5A and 5B, the LEDs are preferably bonded directly to thevertically-oriented micro-cooler (with or without plating such as ENIG,or ENEPIG, Superior plating, USA), and preferably two machined pure(C101 or C110) copper blocks, with mirrored (matching) macro-coolantflow and/or coolant directing channels, “pinching” the vertically laidup etched diffusion bonded micro-channel cooler. Each copper block(which could be in and of itself be a stack of diffusion bonded foils ora solid block) is diffusion bonded to opposing sides of the verticallystacked foil micro-channel cooler 410 in one step. In other words, thefoil layers and blocks are preferably diffusion bonded all in one step.The resultant stack is then preferably machine excised, and the assemblycan then be referred to as the micro-channel cooler assembly, whereasportions of the micro-channel cooler assembly may be referred to asouter capping layer portions (525 and 530) and a micro-channel coolerportion 410. The micro-channel cooler assembly (e.g., outer cappinglayer portions 525 and 530) is/are preferably drilled before performinga machined excision process and before surface finishing process(es)(e.g., a plating process). If a plating process is utilized for thepurpose of providing a solderable surface for the LEDs and/or a wirebondable surface for the wires that attach to the LED bond pads on thepreferable LED top-side, a machined polymer panel is preferably providedthat allows for an o-ring groove (preferable utilizing the sameaforementioned separator gasket/o-ring design) that allows themicro-channel cooler assembly to be clamped to the polymer block and putinto a plating bath with out solution getting into the ID of themicro-channels. This process may also allow for a non-corrosive surfaceto be plated in regions that the anode and/or cathode bus bars 304 a-bmay be eventually clamped or soldered to in the end product. The LEDdriver PCBs 310 a-b may also be edge plated for corrosion reduction andlow voltage drop purposes.

The micro-channel cooler assembly could undergo a quenching or annealingor precipitation hardening process so that pure hardened copper (whichhas an approximately 10% higher thermal conductivity than Glidcop) couldbe used in the foil layers (e.g., foil layer 520). Pure copper wouldenhance solder wetting.

In an embodiment in which the diffusion bonded foil layers (e.g., foillayer 520) are oriented horizontally, the micro-channels ofmicro-channel cooler 410 may be etched in the same plane as the bottomof the LEDs (e.g., LED 531) so the primary inlet/outlet micro-channels(e.g., channel 411) can be etched or even machined in the foil layers.The internal micro-channels of micro-channel cooler 410 may be formedthrough all or substantially all of the diffusion bonded foil layers(e.g., foil layer 520) substantially as deep as the thickness of all thelayers together and/or stopping near or at the bottom of the heatspreader layer 540 may be considered.

Turning now to the positioning of reflector 201, it is preferable thatdielectric spacer layer 514, such as polyimide film, be placed betweenthe bottom surface of the reflector 201 and the micro-channel cooler410. This insulates the reflectors from the micro-channel cooler 410both thermally and electrically, as well as provides a space for thewires (e.g., wire 530) from the LEDs (e.g., LED 531) to fit under thereflector 201 and have the crescent end of the wire affixed to thepreferably gold containing plated copper foil layer 513 that is part ofthe flex-circuit assembly 510, which is directly bonded to themicro-channel cooler 410. As such in one embodiment, the dielectricspacer layer 514 is at least as thick as the thickness of the wires(e.g., wire 530).

Using an automated die bonder such as a Datacon, Austria, MRSI, USA witha tamping tool or even a capillary tool, the wires (e.g., wire 530) canbe automatically tamped (bent) down in such a way as to lower the wireloop until it is substantially parallel (and perhaps even touching thefoil layer on top of the polyimide layer before the crescent terminationpoint) to the flex-circuit 510-polyimide/copper foil layer(s) (a/k/aconductive circuit material layer). The flattened wire does not touchthe anode surface or the edge of the LED (e.g., LED 531) as a shortcould otherwise result. Other manual and/or automatic means may beconsidered, such as one long tamping tool that tamps all of the wires inone step, or the edge reflector itself with or without a dielectriccoating could be employed for this tamping purpose. The primary purposeof this wire-bending step is to allow the reflectors to be placed invery close proximity to the LEDs (e.g., within at least a wire diameter)and to eliminate chafing, touching, or shorting to the reflector 201.The reflectors (e.g., reflector 201) may be preferably designed with anon-imaging software tool such as Photopia, USA. The reflectors may havedifferent operational characteristics such as short to long workingdistances, or short to long depths of field. They should be easilyreplaceable such that they are modular and interchangeable and such thatthey provide the end user with the maximum in operational flexibility.In one embodiment, external dimensions of reflector 201 does notsubstantially change for reflectors configured for differing stand offdistances. For example, as described further below, a reflectoroptimized for a 2 mm focal plane may have substantially similar externaldimensions of a reflector optimized for a 53 mm focal plane.

The reflectors (e.g., reflector 201) may be injection molded fromacrylic, polysulphone, polyolefin, etc. They may be coated with aluminumand/or silver with a dielectric enhancement layers at DSI, USA. They mayalso be extruded from a polymer or metal. It should be noted thatmonolithic reflector halves 201 running the length of the entireassembly of all the UV LED lamp head modules 200 placed end to end(serially in length) may be employed. These long reflectors could havepolished and coated end cap(s) at each end. They could be 5-axismachined from 6061 Al and polished with diamond and a horse hair brush(as the reflectors may be polished) and coated with, for example, asingle layer of MgF2 or SiO₂ optimized, for example (as allaforementioned examples) at 390-400 nm.

One skilled in the art could conceive of any length of LED array 330,reflector 201 and lamp body 305. As described above, one possible lengthof lamp body 305 is approximately 80 mm. This allows for approximately60 45 mil per side LEDs or 68 40 mil per side LEDs, both preferably intwo rows with about a 15 micron (range 5-50 um) gap (e.g., gap 532)between the two rows. A single row or multiple rows (from 1-n) LEDs maybe considered. Even rectangular LEDs that have a longer length along thelong-axis of the LED array may be considered. Along the long-axis, it ispreferable to have less than a 25 micron (range 5-100 um) gap (e.g., gap533). In one embodiment, center-to-center distances between LEDs of theLED array 330 are approximately 10 to 20 microns greater than thecombined edge lengths of neighboring LEDs.

Embodiments of the present invention take into consideration the overallz-axis stack up of the metallic and dielectric layers of theflex-circuit 510 (minus the dielectric spacer layer 514), plus the wirelayer thickness (diameter of each wire or thickness of each wire strip)running above the preferably cathode flex-circuit layer 513 and runningto the rectangular-shaped cathode wire bond pad 534 shown beneath theball bonds of the wires (e.g., wire 530) on the preferably top surfaceof the LEDs.

In one embodiment, the total z-axis stack up is not much thicker thanthe thickness of the LEDs (a/k/a the LED layer). In various embodimentsof the present invention, the LED layer may have a thickness ofapproximately 145 microns and ranging from a thickness of approximately250 microns or less, 200 microns or less, 150 microns or less, 100microns or less, 50 microns or less to 25 microns or less.

In various embodiments of the present invention, in which theflex-circuit layer 510 includes the dielectric spacer layer 514, theflex-circuit layer may have a thickness of approximately 7.8 mil or lessand ranging from a thickness of approximately 12 mil or less, 10 mil orless, 5 mil or less to 3 mil or less.

In various embodiments of the present invention, in which theflex-circuit layer 510 excludes the dielectric spacer layer 514, theflex-circuit layer may have a thickness of approximately 5.3 mil or lessand ranging from a thickness of approximately 10 mil or less, 8 mil orless, 2.5 mil or less to 0.5 mil or less.

In one embodiment, the total z-axis stack up is not much thicker thanthe thickness of the LEDs (a/k/a the LED layer). In various embodimentsof the present invention, the LED layer may have a thickness ofapproximately 145 microns and ranging from a thickness of approximately250 microns or less, 200 microns or less, 150 microns or less, 100microns or less, 50 microns or less to 25 microns or less.

In one embodiment, a bottom surface of the optical reflector 201 isbetween approximately 1-1.5× the thickness of the wire layer above a topsurface of the light emitting device array layer. This allows reflector201 to fit in close proximity to either or both the edge of the LEDs orin relation to the top surface of the LEDs, which thereby maintainsirradiance by maximizing the number of emitted photons that arecontrolled by the reflector 201 and minimizing the number of emittedphotons that escape the reflector 201 by going underneath the reflector201. Locating reflector 201 close to the LED edge also allows for a morecompact reflector in terms of height. This proximity of the reflector201 to the LED array 330 also allows for a shorter length cathode layer513 of the flex-circuit 510, which also allows the cathode layer 513 tobe thin and still carry high current without too much impedance. Thefurther the reflector edge gets from the LED, the taller the reflectorneeds to be according to commonly known optical principles. Althoughslightly higher irradiance could be achieved with taller reflectors,taller reflectors may be impractical in certain implementations.

Additionally, the flex-circuit 510 is inexpensive to manufacture and isvery compact and thin, as such, it is well suited to usage in thecontext of embodiments of the present invention in which the overallz-axis stack up of the metallic and dielectric layers of theflex-circuit are desired to be minimized. Lenthor, USA, is an example ofan excellent flex-circuit manufacturer. In one embodiment, flex-circuit510 may extend beyond the micro-channel cooler assembly and may beconnected (directly or indirectly) to external DC/DC and/or powersupplies.

As described earlier, another novel feature of embodiments of thepresent invention includes the use of a preferably diffusion bonded(though the layers may be soldered or glued or brazed) preferably etchedfoil micro-channel cooler 410 that preferably has a high aspect ratio ofat least one short laterally etched channel(s) (across the shortdirection (width) of the LED array 330) that may be in thermal paralleland preferably arrayed in a side-by-side fashion over a long length, inwhich the coolant flows across and underneath the LED array 330 in thedirection preferably substantially parallel to the shortest dimension(s)of the array 330, usually the width not length dimension. In otherembodiments, the coolant may flow in a direction along the length of theLED array 330 and/or cooler 410, and it may flow vertically (towards thebottom surface of the LEDs) in some areas. In one embodiment, manychannels may flow underneath the bottom of the LEDs and very close tothe bottom of the LEDs separated by only about 125 um of copper (range1-1,000 um), plus a thin layer of solder that is used to bond the LEDdirectly to the common anode substrate 317. Additionally,multi-directional etched coolant paths and orientations, individually orin groups, also described as internal heat transfer channels, runningparallel, perpendicular, vertically, or horizontally, connected, or notconnected, or some combination of both, oriented with respect to thelength or width or some combination or both, of the LED array 330,and/or the bottom surface of the LED(s) may be considered.

According to one embodiment, the internal heat transfer channels may beoriented such that (i) two or more adjacent LEDs in the shortestdimension of the LED array have substantially independent heat transferchannels under each LED and (ii) the LEDs above these channels arecooled independently (i.e., the group of channels under each LED havesubstantially no convective communication with each other or with thegroup of channels under the adjacent LED). Hence, the two or moreadjacent LEDs are said to be cooled in thermal parallel rather than inthermal series. Thermal series would result if the channel flowsubstantially directly underneath the LEDs was commingled or if a commonchannel flowed substantially directly underneath both LEDs.

The foil layers (e.g. foil layer 520) of the micro-channel cooler 410are preferably substantially copper, and they preferably have around 1%(range 0.1-10%) of an interspersed ceramic material such as Al₂O₃ andknown commonly as Glidcop, which is known to maintain its stiffness,strength and shape after being subjected to high diffusion bondingtemperatures. Glidcop is now available having nearly the same thermalconductivity as pure copper.

In one embodiment, the micro-channel cooler 410 is constructed as a highaspect ratio device corresponding to the high aspect ratio of thedirectly mounted LED array 330. This is to say that the cooler 410 has alonger length on which the LED array 330 is mounted along, than it'swidth, and the cooler 410 itself often has many short channels side byside and with flowing coolant in a direction often parallel to the widthof the LED array 330, and perpendicular to the long-axis of the cooler410 (the largest dimension), and that may have 1-n channels located sideby side to one another. Internal micro-channels may be oriented to formmanifolds that are parallel, perpendicular, horizontal and/or verticalto either or both the long-axis (length) or the short-axis (width) ofLED array 330. The foils (e.g., foil layer 520) are then preferablystacked on top of each other (or together) with each channel preferablylocated underneath the channel that is located on or in the foilimmediately above the neighboring foil whether or not the foils arestacked in any vertical or horizontal or other angular or rotationallylocated orientation in a three dimensional space. In one embodiment, theLED(s) are mounted directly to the surface (e.g., a common anodesubstrate) formed by the edges (when the foils are stacked vertically)of a multiple diffusion bonded stacked foil laminate. It is preferablethat the surface formed by the edges of the foil laminate be first madeflat before LED array 330 is soldered to this surface.

As a non-limiting example, the LEDs could be mounted in two (1-n) rowsacross the width, and be on the order of 50 to 300 LEDs along the lengthof the row. The length of the row is preferably around 90% (10-100%) ormore of the length of the cooler 410. That is the LED array 330 extendsas close as possible to the edge of the micro-channel cooler 410. Inthis manner, there is no significant irradiance gap in seriallyconnected UV LED lamp head modules 200. This configuration is mostbeneficial in the context of short working distances (˜2 mm).

It is preferable that the internal micro-channels running beneath theLEDs of LED array 330 have approximately equal flow so that thejunctions of the LEDs are approximately the same temperature. For somespecialized applications the flow could be different in some channels torun LEDs hotter or cooler, especially if the LEDs are of differingwavelength as short wavelength LEDs may require more cooling. It shouldbe noted that not all embodiments require 100% of the coolant runningthrough the micro-channel cooler to run through heat transfer channelsof the micro-channel cooler.

According to one embodiment, CFD is preferably employed to design themain inlet and outlet coolant manifolds formed in base of the body 305to enhance or constrict coolant flow as needed to accomplish theaforementioned desirable nearly equal flow in the micro-channels. CFD ispreferably conducted by MicroVection USA. Enhancement could beaccomplished by making the channels deeper or wider or both, orconversely, constriction could be accomplished by making the channelsshallower or narrower or both. All of these geometries could be threedimensional with simple or compound contours or nearly straight or sharpgeometries. Again, speaking to the micro-channels, they could be ofdiffering size, shape, depth, width, number, center to center spacing,number of etched foil layers, curves, protrusions, squiggles,gull-wings, etc. needed in order to balance flow and or reduce thermalresistance between the channels and the LED junctions.

FIG. 6 is an exploded magnified isometric cut-away view of a top portionof the body 305 of and illustrating various layers of the UV LED lamphead module 200 of FIG. 2. In this example, LED array package 318includes the dielectric spacer layer 514, the cathode layer 513, thedielectric separator layer 512, the adhesive layer 511 and the commonanode substrate layer 317. Flex-circuit 510 could also include an anodelayer (not shown). As described above, layers 511-514 may collectivelyform a flex-circuit 510 from the Pyralux family of product. In oneembodiment, the flex-circuit 510 may not include the dielectric spacerlayer 514, which could be bonded to a bottom surface of the reflector201 or simply be free floating between the bottom surface of thereflector or bonded to a top surface of the flex-circuit 510. Inalternative embodiments, a rigid flex or rigid circuit with a rigiddielectric (e.g., FR4, ceramic, glass or the like) could replaceflex-circuit 510.

In one embodiment, dielectric spacer layer 514 and dielectric separatorlayer 512 comprises a polyimide (e.g., Kapton, available from DuPont,USA), PEN or PET layer. The cathode layer 513 is preferably a copperfoil. Cathode layer 513 and dielectric separator layer 512 preferablyform an integrated layer of cathode foil and dielectric (which is knownas “adhesiveless” in the Pyralux family of products available fromDuPont, USA). As described above, these layers forming LED package 318are pinched between cathode claws 320 a-d and 321 a-b and anode body 315a-b.

One design choice is binning individual UV LED lamp head modules (whichwhen forming serial arrays would typically require connecting lampswithin the same bin) versus binning LEDs within UV LED lamp headmodules. Having the capability to bin within individual UV LED lamp headmodules means one need not bin individual lamps. As noted above, in oneembodiment in which binning is performed within the UV LED lamp headmodule 200, flex-circuit 510 (e.g., comprising an electrically isolated(segmented) cathode layer 511, dielectric separator layer 512 anddielectric spacer layer 514) is employed to potentially individuallyaddress each LED of the LED array 330, or groups of LEDs so that theLEDs may be binned for Vf, wavelength, size, power, etc. in groups from1-n, thereby substantially lowering the demands on the LEDmanufacturer(s) to supply LEDs in just one or a few bins. According toone embodiment, the bins can be about 0.1 Vf or less—and most preferably0.05 Vf or less, or even 0.01 Vf or less. Depending upon the particularimplementation, the LEDs of LED array 330 could be in just one or twolarge Vf bins, such that one or two long strips of LEDs in the arraysare from the substantially same Vf bin. Conversely, the bins could be astight as 0.00001 Vf. In this example, segmentation of the flex-circuitlayer 510 and or the LED driver PCBs 310 a-b could be reduced or eveneliminated. This may be accomplished when very large volumes and orlarge LED chips are produced and there are substantial numbers of LEDsavailable from the manufacturers in Vfs that are close to 0.001 Vf orless.

However, the segmentation of the LED driver PCBs 310 a-b and flexcircuit 510 allows numerous options to bin by Vf values, or not at all.In the present example, the LEDs of LED array 330 are divided into eightindividually addressable groups by locating them within eightflex-circuit segments (four of which are visible in the present view,i.e., segments 611 a-d). In one embodiment the segments 611 a-d areformed by photolithigraphically patterning the cathode layer 513 andetching away the metal foil to form electrical isolation traces (e.g.,electrical isolation trace 610). Dielectric layer 512 in the area belowthe LEDs is removed by laser machining, routing or stamping.

In general, the most suitable UV LED wavelengths are in the range ofabout 360-420 nm, and most preferably ˜395 nm. It should be noted that amix of wavelengths may be use in each UV LED lamp head module 200 andsmaller groups and/or even individual LEDs or some combination of both,may be individually addressed by wire bonding to an individualconductive stripe (not shown) of cathode layer 513 (patterned conductivecircuit material layer) on flex-circuit 510, the conductive stripe(conductive circuit material layer) being preferablyphotolithographically imaged and etched with a preferably polyimide(non-electrically conductive layer a/k/a dielectric layer) beneath it.The cathode layer 513 is usually copper.

According to one embodiment, separator gasket 314 (e.g., monolithico-ring 420) fits in a groove machined or molded into the body 305. Asdepicted in the present example, the groove (or gland) shape machinedinto the body 305 may be roughly described as an “o” with tight radiusesin the corners and a portion running through the middle of the gasket inthe long axis direction. This preferably single-plane gasket design ismade possible by the unique foil layer design in which the etchedinternal passages of the micro-channel cooler 410 for coolant are foundonly in the portion that lies substantially under the LED array 330, andnot in the portions around the areas that fall substantially under theheat spreader peripheral regions. This allows the bottom of thepreferably monolithic micro-channel cooler assembly to be flat andsubstantially parallel to the mating portion of the lamp body 305 thatcontains the groove for the separator gasket 314.

The peripheral regions of the micro-channel cooler assembly noted aboveare best explained as the regions that substantially exist outside ofthe coolant flow areas and/or the regions that exist under thepreferable “o” cross-section seal. A benefit of this design is thatmultiple seals or a seal with differing z-axis planes is avoided. Inessence, a three-dimensional (z-axis on two or more planes) configuredseal is not needed as a more simple planar two-dimensional (z-axis onone plane) seal will suffice. The diffusion bonded foil layers (e.g.,foil 520) are etched with not only heat transfer passages beforediffusion bonding, but also the primary inlet/outlet micro-channels(e.g., primary outlet micro-channel 411) may be etched in an embodimentof the instant invention. Thus, when the foils 520 making up themicro-channel cooler 410 (e.g., 200 micron thickness) and the foilsmaking up the portion of the micro-channel cooler 410 typically havingno heat transfer passages (e.g., solid capping layer 530 and etchedcapping layer 525) are bonded together, a monolithic micro-channelcooler assembly (including micro-channel cooler 410) results that has aflat bottom side that is used to compress the uniquely shaped seal thatexists between the preferably monolithic micro-channel cooler assemblyand the preferably monolithic lamp body 305.

Not shown is an optional monolithic diffusion bonded heat spreader layer(e.g., approximately 0.5 mm thick (range 0.1 to 1 mm)) that may span thetop surface of common anode substrate 317.

FIG. 7 is an exploded magnified isometric cut-away view of a top portionof a reflector 201 of the UV LED lamp head module 200 of FIG. 2.According to one embodiment, the reflector 201 is about the length ofLED array 330, preferably a few mils longer, and the reflector couldinclude end caps 207 a-b. End caps 207 a-b may be affixed to reflector201 with screws and/or magnets (not shown).

In one embodiment, very long reflectors may be employed such that 80 mmlamp module sections are arrayed end-to-end yet the reflectors aremonolithic and as long as perhaps all of the multiple 1-n lamp modulesaffixed end-to-end. This affixing could be done to a common rail likeassembly.

It should be noted that in UV LED curing systems including multiple lamphead modules, reflector 201 could be used in conjunction withmini-reflectors (as described further below) located in the area betweenthe lamp head modules, and more particularly, in the area locatedbetween the respective ends of the LED array on each adjoining lamp headmodule.

In one embodiment, a field replaceable window 340 covers the outputopening of the reflector 201. Window 340 is preferably made from aborosilicate glass with a wide angle UV or visible AR coating. Window340 may be attached to reflector 201 with one or more magnets 342 ifiron containing strip(s) (e.g., window mount 341) are placed on top ofwindow 340. The magnets 342 are preferably placed in correspondingpockets 342 in the reflector 201. Of course, alternative means ofaffixing window 340 to reflector 201 may be considered such as 90 degreeangle bars wherein one portion wraps around and clamps on the glass, anda slotted portion orthogonal to the clamping surface contains screwsthat are located in the side of the reflector 201. In one embodiment,window mount 341 is recessed into the top surface of reflector 201 toprovide alignment and location. In some embodiments, window mount 341may be attached to reflector 201 with screws.

In one embodiment, serial connection of multiple UV LED lamp headmodules 200 may be facilitated by including orthogonally oriented (withrespect to magnets 342) steel pins or magnets in holes 345.Alternatively, the magnets or steel pins (not shown) could be locatedwithin mini-reflectors (not shown).

FIG. 8 is a magnified isometric view of a reflector 201 of the UV LEDlamp head module 200 of FIG. 2 with an end cap removed. This view isintended to illustrate the modularity of reflector 201. In this example,two of four screws 815 are shown that affix the reflector 201 to thelamp body 305. By simply removing these screws 815, a new reflector withdifferent optical properties can be substituted in place of reflector201. In the current example, integral injection molded feet (e.g., foot816) may be used as alignment features for mini-reflectors (discussedbelow) or end caps. Steel screws 815 could be used to orient, alignand/or hold such mini-reflectors in place if, for example, themini-reflectors contained magnets (with their magnetic fields orientedproperly with respect to the screws 815).

Also, locating pins or mated male/female features that extend from thebottom of the reflectors into the micro-channel cooler 410 or vice versamay be employed for ease of alignment of the reflector 201 with respectto LED array 330. These pins or mating features may be part of theinjection molded reflector.

In one embodiment, locating pins, such as pin 805, could be used toalign mini-reflectors or end cap reflectors. Screws 810 could be used toaffix end cap reflectors to reflector 201.

Protective housing 202 is shown that preferably injection molded andeach half may be a mirror image of the other.

FIGS. 9A-B are isometric views of four interconnected UV LED lamp headmodules 200 a-d in accordance with an embodiment of the presentinvention. In one embodiment, each UV LED lamp head modules 200 a-d maybe designed to be mounted to a common mounting rail (not shown),associated with a customer's UV curing apparatus or machine. Tofacilitate the serial length-wise integration of UV LED lamp headmodules 200 a-d (from 1 to n in number) mini-reflectors (e.g.,mini-reflectors 910 a-c) are provided to allow for the ability to obtainan essentially contiguous beam pattern on the work piece withessentially no discernable irradiance loss in the area between each UVLED lamp head module 200 a-d (e.g., the area below mini-reflectorportion 910 a-c on the work piece surface). Because photons can exit anLED at any angle, it is possible for a photon to traverse the entirelength of serially connected UV LED lamp head modules before exiting thewindow.

The window(s) 340 could have a physical gap in length (e.g., every 320mm assuming 4 80 mm length UV LED lamp head modules 200). In analternative embodiment, windows 340 could be 80 mm long as such therewould be three gaps in 320 mm, each of which could be covered by aseparate mini-window (not shown). The separate mini-windows could beinstalled over these physical gaps and be affixed via a magnetic strip(not shown) or other mechanically fastened strip and result in a dust orforeign material ingress prevention. Other manufacturers use an indexmatching fluid or adhesive; however, as mentioned previously, thesematerials (available from Schott, Germany and Dow, USA) can yellow ordegrade. In one embodiment, one or both of separate mini-windows andreflective index matching fluid and/or adhesive may be employed.

The major and mini-reflectors could be affixed to each other with theirown mini slotted rail that could run between each main reflector withthe mini reflector underneath the rail and between the major reflectors.The major reflectors are defined as the longest portions of thereflector halves that exist in the assembly considered for variousapplications. Long assemblies for wide format printing and flooring, andshort reflectors for applications such as surgical mask componentadhesive curing may be considered.

In connection with interconnecting multiple UV LED lamp head modules,intervening end-caps are removed and mini-reflectors (e.g.,mini-reflectors 910 a-c) are inserted in place thereof between the UVLED lamp head modules to be serially connected. The mini-reflectors 910a-c serve to create uniform irradiance pattern on the work piece andavoid areas lacking in irradiance, which would otherwise create adifference in peak irradiance along the length of the projected beam onthe work piece when serially connected UV LED lamp head modules 200 areemployed. This could have deleterious process effects.

In order to provide this essentially uniform irradiance between LEDlamps, several novel means may be considered. Firstly, the reflectorend-caps between the lamps may be removed. The distance between the twoLED arrays may be ˜6 mm, range 0.1-100 mm. Small ˜6 mm reflectorsubsection(s) (e.g., mini-reflector 910 a-c) could be placed between thetwo main reflectors, the mini-reflectors 910 a-c may have substantiallythe same shape as the main reflectors. As described above, themini-reflectors 910 a-c may also have locating pins, screws, tie-barsand/or beams (not shown) in the perpendicular plane (across theopposite-side reflector halves) and/or parallel planes (parallel to thesame-side reflector halves and serving to connect them together). Smalltie-bars (not shown) that are screwed in place may be strategicallyplaced between the reflector halves for purposes of mechanical rigidityand separator gasket 314 or o-ring 420 loading. These tie-bars, if used,should be of a stiff, high modulus material with minimal cross sectionexposed to the photons emitted from the LEDs. This will minimize anyimpact that the tie-bars may have on the projected beam and its ultimateirradiance uniformity on the work piece, as one would like to avoidinterrupting or blocking the trajectory of emitted photons as much as ispractically possible. The reflectors (e.g., reflector 201) arepreferably two separate halves that are affixed to the micro-coolerassembly with their polished and curved portions facing each other, andthey may have locating pins and it may be easy to interchange reflectorswith screw attachment (e.g., screw 815), so that different reflectorswith differing optical properties may be easily interchanged betweenlamp assemblies. Alternatively, the mini-reflectors 910 a-c could bescrewless (fastenerless) and magnetic holding cylinders could beemployed to mechanically couple the mini-reflectors 910 a-c to the mainreflectors 200 a-d. Additionally, a magnetic (e.g., a laser-cut steel)strip (e.g., window mount 341) that holds the window in place could havelocating pins (not shown) that could be molded into the top surface ofthe reflector and poke through holes in the window mount 341 and serveto locate the output portions of all the reflectors in an essentiallycontiguous straight line. FIG. 7 shows that window mount 341 is recessedinto the top surface of reflector 201 to provide additional alignmentand location. The mini-reflectors may be attached to lamp body 305 viascrews.

Turning now to FIGS. 10A-C an alternative embodiment of an LED arraypackage (e.g., an LED array 1015 coupled to a flex-circuit (not shown)and a heat spreader layer 1030) is now described. This alternativeembodiment is provided to illustrate, among other things, that thepinching/clamping function of cathode claws 320 a-d and 321 a-d can beaccomplished with connectors having differing geometries. In the presentexample, cathode bus bars, e.g., cathode bus bar 1010 and monolithicanodic lamp body 1020 are pinching/clamping the anode heat spreaderlayer 1030 and the cathode flex-circuit layer 1040 together.Additionally, holes, e.g., holes 1050, may be formed in these layers toallow anode and cathode wires 1051 to pass there through, or conductivescrews with or without a dielectric sleeve.

In one embodiment, massively parallel (e.g., substantially all LEDs ofthe LED array are electrically paralleled) high current density UV LEDs(SemiLEDs, USA) may be directly mounted on a common copper anode plate1030. Individual or groups of LEDs may be addressed by flex-circuit(which aids in manufacturing flexibility with regards to binningrequirements for Vf, power, wavelength, etc.). A high aspect ratio LEDarray (with a length longer than width which allows for a narrowconcentrated output beam), high-fill-factor array (which allows forconservation of brightness), modular macro-reflectors (which controls amuch higher percentage of photons than micro-reflectors and allow enduser flexibility for applications from close to far working distances,power densities, and depth of field). In one embodiment, a two sidedrectangular opposing elliptical reflector shape (wherein the centerportion is wider than the input and output apertures) allows for a verytightly focused beam.

Anode substrate 1030 is bolted to a replaceable lamp body 1020 that hasat least one liquid flow channel (e.g., channels 1045) that has a highheat transfer coefficient for low thermal resistance (this allows theLEDs to be operated at high current in a high fill-factor array).Additionally the anode plate 1030 (a/k/a sub-mount) is attached to thelamp body (a/k/a lower heat sink segment which may be machined orinjection molded) in a “clam shell” arrangement (affording an easy meansof sealing by compressing the formed o-ring (e.g., o-rings 420 a-c)(Apple Rubber Products, USA) and low thermal resistance as the liquidcoolant can intimately contact the anode plate 1030.

Individual cathode bus bars (e.g., cathode bus bar 1010) are boltedthrough the anode substrate 1030 making electrical contact with thecathode flex-circuit 1040 and at the same time holding the anode 1030tightly to the lamp body 1020 and/or anode bus bar (in effect the anodeplate 1030 with the cathode flex-circuit 1040 is “pinched” between thelower anode bus bar 1030 and upper cathode bus bar 1010—the lower anodebus bar 1030 actually is the anode substrate 1030 of the LED driverboards (not shown).

In one embodiment, a Kapton (dielectric) spacer layer between reflector1011 and cathode flex-circuit foil 1040 allows for the wires (not shown)that connect the LEDs to the cathode foil 1040 to be bent under and“clear” the long (rectangular shaped) reflector edge. It alsoelectrically isolates the reflector if the reflector should be aluminumor have a metallic coating such as silver, groups of LEDs are powered bytheir own driver chips, such as LM 3433 (National Semiconductor, USA),which are part of DC/DC power supplies (allowing for driving the groupswith varying power, most due to varying Vf bin). In some embodiments,power supplies that go directly from AC to DC output in the 4-5V rangecan be considered.

In one embodiment, no significant number of LEDs are connected in series(thus a single LED failure cannot bring down a whole string andelectrically inefficient load balance resistors are not needed). Thebottom of the anode plate 1030 has chemically etched channels 1045 forcoolant flow (thus allowing lower thermal resistance), having alead-free (tin containing solder) on the backside (bottom) of the chipallow for simple and highly reliable vapor phase reflow (to insure thatthe large number of LEDs are uniformly bonded to the anode plate 1030).

In one embodiment, the vapor phase reflow process involves use of avapor phase oven. In one embodiment, a tacky flux (Tack-Flux 7 availablefrom Indium Corporation, USA) is used to tack the LEDs of the LED arrayin place prior to placing the micro-channel cooler assembly in the vaporphase oven. A vapor phase oven uses an inert liquid that when heatedcreates a very stable uniform heat transfer medium in the form of vapor.This medium replaces heat energy very quickly and transfers heat to themicro-channel cooler assembly by condensing this heated vapor. Themaximum temperature that the micro-channel cooler assembly reaches istied to the boiling point of the inert liquid. The boiling point must behigher than the solder melting temperature. A very isothermaltemperature is reached across the entire micro-channel cooler assemblythereby creating one of the most reliable and repeatable solder reflowprocesses known.

Molded polymer screws can attach the cathode bus bars 1010 to the anodesubstrate 1030 through holes in the anode plate 1030/flex-circuitassembly 1040 (thereby eliminating any worry of shorting due to theirpolymer nature and they are low cost due to the use of molding), veryflexible ultra-high strand count wire 1011 (CableCo, USA) may be used tocarry the current to the LEDs (thereby reducing resistivity and strain).Very flexible coolant tubing may be placed into holes in the lamp body1020 (lower heat sink) at opposite ends of the lamp (allowinglongitudinal coolant flow, compact assembly, and low stressconnections).

FIG. 10B Illustrates the alternative LED array package of FIG. 10A witha macro-reflector 1001 in accordance with an embodiment of the presentinvention. In this view, one cathode bus bar 1010 is removed to show acathode wire 1011 coming up through the assembly to make contact withthe removed cathode bus bar (not shown).

FIG. 10C is an isometric view depicting the bottom-side of the heatspreader layer 1030 of FIGS. 10A and 10B. This view depicts the removedcathode bus bar 1010 and micro-channels 1045 etched into the bottomsurface of heat spreader layer 1030 to facilitate heat transfer throughheat spreader layer 1030 by effecting the flow of coolant flow (e.g.,via coolant fluid turbulation).

Referring now to FIG. 10D an alternative embodiment of a UV LED lamphead module 1099 is now described. This alternative embodiment isprovided to illustrate, among other things, an alternative configurationof an etched foil sheet micro-channel cooler 1098, heat spreader layer1090 (approximately 0.5 mm thick), anode bus bars 1091 a-b, cathode busbars (e.g., cathode bus bar 1094), deep and long primary coolant inletand outlet channels 1093 a-b within lamp body 1095, and a single-planeseparator gasket 1097. In this example, rather than having integratedLED drivers, wires (e.g., wire 1092) are provided to individuallyaddress LEDs of LED array 1096. In alternative embodiments, the wirescould be replaced with flex-circuit (not shown) to address individualgroups of LEDs.

Turning now to FIGS. 10E-G yet another alternative embodiment of a UVLED lamp head module 1000 is now described. According to the presentexample, a “t”-shaped micro-channel cooler assembly (1068 and 1067) isshown, supported by optional outer foil layer areas 1075 and 1076. Inone embodiment, the micro-channel cooler 1068, the heat spreader layer1067 and outer foil layer areas 1075 and 1076 form a replaceablemonolithic micro-channel cooler assembly.

According to the present example, a copper anode substrate (which couldbe considered a thick foil layer) is provided by the “t”-shapedmicro-channel cooler assembly 1067 and 1068, which is diffusion bondedto lateral (lying flat) sheets of copper/alumina with etchedmicro-channels 1090 to make a single monolithic high thermalconductivity part.

In this example, the top of the “t” is the heat spreader layer 1067 andthe vertical part of the “t” are the stacks of foil 1068 with etchedchannels. The two parts of the “t” are preferably diffusion bondedtogether after, or possibly in conjunction with, the bonding of the foillayers 1070. In this instance, a multi-plane seal (similar to thesingle-plane seal provided by o-rings 420 a-c) may need to beconsidered, with a section under the etched foil layers (near thepreviously mentioned o-rings) that prevents bypass being in a differentplane as the peripheral regions around the bottom of the heat spreaderplate that prevent the flow of liquid to the surrounding outsideenvironment. One could construct a mating lamp body to accommodate thesefeatures and construction. A difficulty may arise in preventing fluidbypass around the ends of the vertical “t” portion consisting of theetched foil diffusion bonded layers and lamp body 1062 that may containa main coolant inlet channel 1063 and a main coolant outlet channel1064. This is to say that fluid could potentially, without another meansof sealing this region, flow from one channel 1063 to the other 1064without going through the micro-channels 1090. This could be preventedby having the seal run vertically in the portion at either end of thefoil stack, or perhaps glue or solder could be considered. The verticalstack of foiled could be diffusion bonded, brazed, glued or soldered tothe bottom of the heat spreader layer as well. There could be anintermediate layer between the lamp body 1062 and the heat spreaderlayer 1067 that runs around the periphery of the area between the lampbody 1062 and the heat spreader layer 1067 that has a z-axis height thatis substantially the same height as the vertical t-portion consisting ofthe stacked etched foil micro-channel layers 1068.

In this example, main coolant inlet channel 1063 and main coolant outletchannel 1064 run parallel to the high aspect ratio long axis length ofthe LED array 1071 (which is bonded to the copper anode substrate withan optional intermediate heat spreader layer 1067). In one embodiment,coolant inlet and outlet tubes 1080 are provided at opposite ends of theparallel but opposing main channels 1063 and 1064, thereby creating amanifolding arrangement wherein the micro-channels 1090 havesubstantially uniform coolant flow.

Monolithic anodic bodies 1061 a-b are attached to the lamp body 1062with polymer bolts clamping the separate cathodic bus bars 1060 a-b tothe anodic bodies 1061 a-b with the cathode flex circuit foil bonded tothe anode substrate (1068 and 1067) pinched in between. This pinchingalso compresses the o-ring 1069, and prevents coolant bypass, as well ascoolant leakage to the outside environment.

The monolithic anode bodies 1061 a-b directly oppose each other and areattached, and in thermal communication, to the sides of lamp body 1062,parallel to the main inlet and outlet flow channels 1063 and 1064, andperpendicular to, and in electrical communication with the copper anodesubstrate 1068 and 1067, that is itself clamped between the anode bodies1061 a-b and the cathode bus bars 1060 a-b by polymer bolts. Thisconfiguration provides extremely low thermal resistance and its inherentisothermal nature, combine to allow a practical means for operating ahigh fill-factor, high density, high power, and high brightness UV LEDarray in a practical manner.

The heat spreader substrate 1067 could in itself be considered a foillayer. One may allow heat spreading to take place simply in thedistances between the layers and/or between the etched channels. Itshould be noted that the vertical orientation of the layers can providelower thermal resistance, but has differing ease of assembly andapparatus functionality. Squiggles, or bends, or “gull-wings” in thechannels and in, or with interconnecting channels, may be advantageouslyconsidered, as may etched protuberances or varying widths and depths ofchannels for the purpose of turbulence generation or boundary layercompression. It is preferable to have the substrate (a/k/aheat-spreader, if one is indeed employed) strike a balance betweenspreading thermal energy, yet not being so thick that it addssubstantially to the overall thermal resistance between the LED junctionand the flowing coolant. Also, it should not be so thin as to bemechanically flexed by the internal pressure or turbulence of theflowing coolant, hence, it is reasonable to make the substrate about 125um to 250 um thick, range of 10-1000 um, and to have about 8-16 foillayers, range 1-100, that are about 25-50 um thick, range 1-500 um, andhave channel etched depth of about 12.5-25 um, range 1-500 um, andcenter-to-centers of about 30-60 um, range 1-1000 um, and finally achannel length of about 4000-4300 um, range 1-100000 um. The coolers maybe plated internally or externally for the purpose of erosion,biofouling, corrosion, and/or electrical impedance reduction. Internalcoating should generally be avoided as they can flake off later anddeleteriously impact cooler lifetime. The foil layers could be made of amaterial such as nickel that is more erosion resistant, and/or the couldbe coated with a ceramic or metal in a conformal coating process such asALD, preferably post diffusion bonding. It should be noted that it iscommon to pre-plate the layers with nickel prior to diffusion bonding. Amicron, or sub-micron range filter can be employed either up ordownstream or both from the cooler, and a deep UV C light source, suchas a lamp or LED, could be employed for the purpose of the reduction ofbio-fouling. Preferably 0.1-15 micron filters may be employed from 3M,USA, and/or membrane contractors from Membrana, USA that are veryeffective at removing carbon dioxide, which can have a deleteriouseffect on the pH of the cooling fluid and increase corrosion.

FIG. 11A conceptually illustrates a cross-section of twomacro-reflectors 1110 a-b and 1120 a-b superimposed on top of each otherin accordance with an embodiment of the present invention. In thisexample, the macro-reflectors 1110 a-b and 1120 a-b have substantiallythe same external height and width but are optimized for differentworking distances. Having a single deep trough macro reflector lengthand then having differing internal curved surfaces for differing focusesis efficient from a manufacturing standpoint as only a single outer moldis needed and differing curves are simply differing mold inserts.

In the present example, macro-reflector 1110 a-b is optimized for a 53mm focal plane 1140 and macro-reflector 1120 a-b is optimized for a 2 mmfocal plane 1130. Each curved portion shown is a mirror image of theother (assuming they have the same focal length) and represent a portionof a complete ellipse, parabola and/or a combination of the two. Aparabola is a special case of an ellipse and would generally be used forcollimating light.

An ellipse has two focuses, a primary focus and a secondary focus. Inthe current example, the primary focus is in the LED plane 1170 and thesecondary focus is in the work piece plane 1130 or 1140.

In various embodiments of the present invention, marginal ray 1111(representing the first ray captured by reflector 1110 a) and the lastray (not shown) captured by reflector 1110 a and exiting an LED arraydefine an angular extent 1150 of approximately between 60 to 89 degreesand preferably 80 to 85 degrees, thereby exemplifying (using asimplistic 2-dimensional analysis) that the 53 mm macro-reflector 1110a-b controls more than approximately 80% of the photons that leave theLED array. In fact, 3-dimensional computer analysis suggests such a deeptrough reflector design (when end caps (e.g., end caps 207 a-b) are inplace) controls over 90% of the photons that leave the LED array. Thelarger the angular extent the greater control over the photons that exitthe LEDs. Therefore, angular extent can be increased, but practicalconsiderations for reflector sizes (lengths and widths) need to be takeninto consideration.

With reference to FIG. 11B it can be seen that marginal rays 1121 a-b(representing the first ray captured by reflector 1120 a and the lastray captured by reflector 1120 a, respectively) exiting LEDs 1150 a and1150 b and reflecting off reflector 1120 a define an angular extent 1160of approximately between 65 to 89 degrees and preferably 82 to 87degrees, thereby exemplifying (using a simplistic 2-dimensionalanalysis) that the 2 mm macro-reflector 1120 a-b controls more than 82%of the photons that leave the LED array in accordance with an embodimentof the present invention. In fact, 3-dimensional computer analysissuggests such a deep trough reflector design (when end caps (e.g., endcaps 207 a-b) are in place) controls over 96% of the photons that leavethe LED array.

FIG. 12 shows a portion of macro-reflector 1210 optimized for a 2 mmfocal plane 1240 in which each side of the reflector has a focal point1220 that is offset from a centerline 1231 of a focused beam 1230(having a total pattern width of approximately 7 mm and a highirradiance center portion of approximately 0.65 cm) on a work piece (notshown) in accordance with an embodiment of the present invention. Asdepicted in the drawing, in such a configuration, reflected light raysfrom the right-hand side reflector move from the left of the centerline1231 inward toward the center and reflected light rays from theleft-hand side reflector move from the right of the centerline 1231inward toward the center. In this manner, the two sets of reflectedlight rays overlap to create the high irradiance beam 1230. Computermodeling indicates about a 10% higher irradiance level than if the twosets of reflected light rays did not overlap. Notably, in oneembodiment, at longer focal planes distances (e.g., ˜53 mm), there is nosignificant loss (less than 5%) of irradiance at planes+/−3 mm from thefocal point.

FIG. 13 is a graph illustrating estimated convective thermal resistancefor various channel widths. This figure graphically depicts the lineardecrease in thermal resistance with decreasing width of individualmicro-channels. Of note is the fact that embodiments of the presentinvention usually use channels having widths of less than 0.1 mm, andoften 0.05 mm, 0.025 mm or less. This is contrasted with the width ofchannels used in prior art UV LED lamp devices, such as thosemanufactured by Phoeseon (USA) and Integration Technology (UK), whichare believed to use macro-channels on the order of 0.5 mm or larger.Meanwhile, such prior art UV LED lamp devices also suffer from highcontact resistances at the point at which the LED array is attached to aseparate cooler. They also suffer from the high bulk thermal resistanceof the substrate that the LED array is attached to.

As can be seen from the graph, all else being equal, the order ofmagnitude decrease in thermal resistance from a 0.55 mm channel to a0.025 mm channel would in and of itself result in an order of magnitudedecrease in LED junction temperature. However, all else is not equal. Ascurrently understood by the inventors, the prior art has only onethermally-related factor working in its favor. This factor being the useof a low brightness, low fill-factor (LED packing density) array, whichspreads out the heat sources and results in a low thermal density, whichrequires a correspondingly lower heat transfer coefficient for the samejunction temperature.

Working against prior art UV LED curing systems, however, is the factthat they typically employ a series/parallel LED arrangement whichresults in the need for a thermally resistive dielectric layer betweenthe chip bond pad and the substrate. It should be noted that even if ahigh thermal conductivity (expensive) dielectric, such as DLC, was used,there still is additional contact resistance at both interfaces, whichoften exceeds the bulk thermal resistance of the dielectric. Secondly,Phoseon uses a silicon substrate which has less than half the thermalconductivity of copper. To our knowledge, Phoseon also then bonds thissilicon substrate to a copper heat exchanger creating even more thermalresistance. In fact, all of these thermal resistances add up to a pointwhere even if a micro-channel cooler were to be used in such anenvironment, the benefits of the micro-channel cooler's lower thermalresistance would be seriously compromised. As for Integration Technology(whose LED arrays are currently produced by Enfis Group PLC, UK), theirtechnology at least does not use a silicon substrate, perhaps an AlNsubstrate (about half the thermal conductivity of copper) or they mightuse a thick (e.g., approximately 1 mm) copper substrate. A DLCdielectric layer could have a very small, but quantifiable benefit asDLC has high bulk thermal conductivity, but the layer is so thin and thecontact resistances are so great so as to overwhelm the benefits gainedby the very high bulk thermal conductivity of DLC. Hence, prior art UVLED systems suffer a seriously high thermal resistance compared toembodiments of the present invention in which no bond pad, trace anddielectric thermal resistance degradation issues are created owing tothe fact that no bond pad, trace and dielectric is used between theLED(s) (e.g., LED 531) and substrate (e.g., common anode substrate 317)nor required due to the purely parallel LED electrical arrangement.Additionally, embodiments of the present invention minimize bulk thermalresistance loss through the copper substrate due to the minimal (usuallyabout 125 um (range 5-5,000 um)) thickness between the bottom surface ofthe LEDs and the heat transfer passages (micro-channels) no extrainterfacial resistances from bond pad layers. The higher voltage ofelectrically-seriesed LEDs can lead to some AC/DC conversionefficiencies and cable resistance reductions (for a given cablediameter).

FIG. 14 is a graph illustrating output power for various junctiontemperatures. This figure shows the severe drop off in UV LED efficiencywith increasing junction temperature. A drop of inefficiency of 40% isnoted with a junction temperature increase from 20 to 88 degrees C. UVLEDs are much more sensitive to heat than some longer wavelength blueand green LEDs. Hence, it is desirable to use superior thermalmanagement in order to keep the junction temperatures low to achieveboth long life and maintain a reasonable efficiency.

In accordance with embodiments of the present invention, LED junctiontemperatures of approximately 40-45 degrees C. are obtained, even whenoperating at current densities of over 2.5 A/mm², and sometimes over 3A/mm². This may be contrasted with the UV LED lamp heads of Phoseon andIntegration Technology that probably operate at current densities ofless than 1.5 A/mm², with LEDs spaced much further apart (lowfill-factor/low packing density), which of course leads to lower peakirradiance and lower total energy delivered to the work piece.

FIG. 15 is a graph illustrating a dynamic resistance vs. forward currentcurve for a typical LED on a typical heat sink. It is to be noted howthe dynamic resistance approaches an asymptote as the current approaches1500 mA. This is illustrative of several factors, including thedeleterious impact of a temperature difference between any two LEDs inan electrically-paralleled LED array. Since a negative temperaturecoefficient of electrical resistance is inherent to LEDs, the graphshows that just a small change in (dynamic) resistance can have a largeaffect on current. Therefore, it is desirable to create a substantiallyisothermal substrate upon which the LEDs may be mounted. For example,the LEDs may be mounted on a substrate that has low thermal resistance(as well as mounted with low thermal resistance direct solderingtechnique), high thermal conductivity, high heat transfer coefficient(10,000-35,000 W/m²K), and high thermal diffusivity (thermalconductivity divided by heat capacity) in order to create a nearlyisothermal condition between substantially all of the paralleled LEDjunctions.

A micro-channel cooler with a short thermal diffusion length (e.g.,approximately 125 microns) between the LED(s) and the coolant channels(heat transfer channels) ideally meets these conditions. Thermaldiffusivity is a measure of the rate at which a temperature disturbanceat one point in a body travels to another point. By way of analogy, byrapidly diffusing a temperature rise that exists in one LED and rapidlytransferring this energy to its surroundings, keeps all of the LEDsessentially isothermal. In reality, “essentially”, is a relative term,as the upstream LEDs (near where the coolant enters the lamp body, aswell as nearest where the coolant enters the heat transfer channels) maybe at some small to infinitesimally small lower temperature as a resultof the design of the micro-channel cooler employed. In one embodiment,heat transfer channels of the micro-channel cooler are designed so thatthe passages are in thermal parallel (i.e., there is essentially notemperature difference between the LEDs as the coolant flows under the(e.g., 2 rows of) LEDs in parallel not series. As such, there is lesslikely to be a temperature difference.

However, to the extent that there is a difference in Vf and output powerwithin a bin of LEDs, such differences can be dealt with via a uniqueelement of embodiments of the present invention in that the wholeupstream bank (row) of LEDs, as well as each segment of the upstreamrow, can be individually addressed. Therefore, LEDs with a pretestedhigher/lower Vf (impedance) and/or higher/lower output power can bestrategically placed near the higher/lower temperature coolantexit/entrance areas (whether they be primary coolant inlets/outlets 360and 316 or internal micro-channels). Also, LEDs with varying operatingcharacteristics, including, but not limited to Vf, wavelength, opticalpower and the like can be employed.

According to one embodiment, LED driver PCB 310 does not work on dynamicresistance, nor voltage, but current. The current-mode operationmeasures current and through (e.g., tiny 0.005 Ohm) resistors amplifies,measures and feeds that current information back into the control loop.The current ripple is designed to be a maximum of (e.g., 10%) full load,or 0.3 A if operated at 3 A per LED. This maximum ripple is worst case,as it does not include the output capacitors which will further reducethe ripple.

Dynamic resistance is simply Vf/If. For example, if Vf is 4.5V at 3 A,it is 1.5 Ohms per LED. Since resistances divide in parallel, one candivide 1.5 Ohms by (e.g., 17 LEDs) to get (e.g., 88 mOhms) dynamicresistance at 51 A for the whole driver. In one embodiment, and asdescribed further below, each segment has its own driver IC(s), eachdriver segment can drive accurate currents even in short, meaning we canshort the output, driving at 51 A and the voltage across the short willbe zero. The driver does not differentiate among output voltages, itjust maintains the current at which it is set. If opened, the outputwill go to the input voltage of (e.g., 12V). If shorted, it will go tosomewhere very close to zero volts. The LEDs are somewhere in-betweenthe range of about (e.g., 4-4.5V). K factor is the change in Vf dividedby the change in junction temperature of an LED. K factors may beconsidered in connection with designing UV LED lamp head modules.Smaller K factors indicate a lower thermal resistance package.

With respect to individual LEDs, the exceptionally low thermalresistance in the range of approximately 0.05K-cm²/W to 0.01 K-cm²/W andpreferably approximately 0.020 K-cm²/W or less helps; however, binningis still helpful. An individual LED with a lower natural dynamicresistance will draw more current/heat than its neighbors, if it heatsmore, then its resistance decreases and it runs away—meaning that thecycle continues until the LED burns itself out (opening). Low thermalresistance keeps all of the LEDs thermally monolithic (isothermal),which keeps the dynamic resistance delta low and dramatically reducesthe chance of run-away. With a low-enough thermal resistance (e.g., inthe range of approximately 0.05K-cm²/W to 0.005 K-cm²/W), one couldconsider each of the parallel and closely binned groups of LEDs as one.The tighter the Vf binning (i.e., 0.01, 0.001, 0.0001V), the less likelyit is for any given LED in a bin to run at a high enough output power(owing to its disproportionate current draw) to shorten its lifetimerelative to other LEDs in the same bin.

The asymptotic nature of dynamic resistance is the same as the asymptoteof Vf. The harder the LED bank is driven, it requires exponentially lesschange in voltage to affect the drive current. In LEDs driven with avoltage-mode driver, when Vf decreases because of temperature therewould be an exponential change in current and a runaway could ensue ifthe voltage was not pulled back. However, because in various embodimentsof the present invention, LED driver PCBs 310 are constant current-modedrivers, voltage (and therefore resistance) does not matter.

FIG. 16 is a graph illustrating an irradiance profile for a UV LED lamphead with a reflector optimized for a 2 mm focal plane in accordancewith an embodiment of the present invention. According to the presentexample, maximum (peak) irradiance of approximately 84.8 W/cm² isachieved with an output beam pattern width of approximately 0.65 cm andproducing an average irradiance across the width of the output beampattern of approximately 31.6 W/cm² and total output power ofapproximately 20.5 W per cm of output beam pattern length. This examplewas generated with a computer model assuming the use of SemiLEDs'˜1.07×1.07 mm LEDs, with each LED producing 300 mW output at 350 mA. Itis to be noted that embodiments of the present invention could run eachLED at higher current (e.g., approximately 2.5 A) at approximately 0.75W to 1.25 W.

FIG. 17 is a graph illustrating an irradiance profile for a UV LED lamphead with a reflector optimized for a 53 mm focal plane in accordancewith an embodiment of the present invention. According to the presentexample, maximum (peak) irradiance of approximately 24 W/cm² is achievedwith an output beam pattern width of approximately 3.65 cm and producingan average irradiance across the width of the output beam pattern ofapproximately 5.9 W/cm² and total output power of approximately 21.7 Wper cm of output beam pattern length. This example was generated with acomputer model assuming the use of SemiLEDs' ˜1.07×1.07 mm LEDs, witheach LED producing 300 mW output at 350 mA. It is to be noted thatembodiments of the present invention could run each LED at highercurrent (e.g., approximately 2.5 A) at approximately 0.75 W to 1.25 W.

According to one embodiment, in which LED drivers are integrated withinthe UV LED lamp head module, off the shelf AC/DC power supplies designedfor high volume “server farms” may be used. Exemplary front end suppliesare available from Lineage Power USA model CAR2512FP series 2500 W powersupplies. Preferable supplies are Power-One LPS100 12V 1100 W single fanserver supplies that are highly efficient platinum rated front-end AC/DCpower supplies that have power factor correction, may be in electricalparallel, and have a GUI i2C interface, the Lineage power supplies areavailable with a subsystem that incorporates four of these unitsoff-the-shelf (OTS). In 2011 these Lineage units will be similar butwith conduction cooling (without fans).

According to embodiments of the present invention, in addition tocooling the integrated drivers, the coolant water may also beadvantageously employed to cool these power supplies simply by runningthe coolant line through a heat sink in communication with the elements(or the base plate) of the supply that need cooling. It is optimal toderate these Lineage supplies as they are more efficient at a percentageof their maximum power. By way of a non-limiting example, running eachPCB with ˜15 drivers at ˜40 amps and ˜4-5 volts one would use about 60%of the ˜10000 W available. It is optimal to design for ˜50 A or greaterand ˜5.5 V to have some headroom now and into the future when thepreferably ˜16 LEDs that are around ˜1000-1200 um square on each of allfour sides (though they could be of any size and shape such asrectangular, or larger size such as ˜2000 um or ˜4000 um or larger perside) are desired to be operated at a current of ˜3 A per LED or ˜48 pergroup solely by way of a non-limiting example. In one embodiment, thecathode bus bars 313 a-b on each PCB 310 a-b near the backside of thelamp body 305 could run nearly the length of the preferably ˜300 mm longboard (not shown) as well as solder pads running nearly the length ofthe PCB. In one embodiment, the cathode cross plate 375 represents a tiebar affixed across cathode bus bars 313 a-b which provides an effectiveattach point for the preferably single main cathode wire 205 going fromthe UV LED lamp head module 200 to the AC/DC power supplies preferablyin somewhat similar fashion to the preferable single main large AWGrange ˜1-10 and preferably ˜2 AWG core anode wire going from thepreferably constant current (CC) DC PCB boards of the UV LED lamp headmodule 200 to the supplies that are preferably connected to the AC mainsto give a highly efficient power source to the LEDs with low ripplepreferably less than 10% to maximize LED lifetime. On the PCB there maybe some shared components of the aforementioned non limiting example of˜15 CC drivers such that there would not be a definitive requirement for˜15 separate components that may not have to have their cathodesisolated. It should again be noted that 1-n cathode and anode cables mayfeed the lamp with electrical power from 1-n power supplies or mains. Itmay be preferable to use four Lineage USA 2500 W power supplies per lampand run them at derated power for efficiency. They are available with acommon back end for ˜4 power supplies. With or without the back end fourseparate anodes and cathode wires/cables per lamp may be considered soas to allow the use of smaller diameter cables (methode/cableco, USA)and or large cables and less resistive losses.

In view of the foregoing, it can be seen that embodiments of the presentinvention are predicated on closely spaced array(s) of LEDs, also knownas high fill-factor arrays, so that maximum brightness can be obtained.This is to say that the optical power per unit area per solid angle ismaximized, as brightness may be roughly defined as power per unit areaper solid angle. This high brightness also correlates nearly linearlywith heat flux/thermal demand as the waste heat from the electrical tooptical power conversion becomes more dense as the array densityincreases. Embodiments of the present invention preferably utilize afill-factor array of LEDs of equal or greater than 90%, but has a rangeof 30-100%. The application of a high fill-factor array in accordancewith embodiments of the present invention lead to an extremely high anddense heat load on the order of 1000 W/cm² or more, range 100-10,000W/cm². This high thermal flux is an artifact of the high brightness,i.e. the LEDs are in very close (1-1000 um) proximity to each other,operated at currents of 2-3 or more amps per square mm, (range 0.1 to100 A), which results in extremely high heat flux demands, and of courseconcomitantly requires extremely low thermal resistance coolingtechnology that combines both a very high degree of cooling (e.g.,convective cooling and/or conductive cooling (e.g., thin and highconductivity layers between the LED and flowing gas or liquid)) toachieve junction temperatures that are preferably as low as 40 C or lessfor long life and efficient operation at extremely high output power.

While embodiments of the invention have been illustrated and described,it will be clear that the invention is not limited to these embodimentsonly. Numerous modifications, changes, variations, substitutions, andequivalents will be apparent to those skilled in the art, withoutdeparting from the spirit and scope of the invention, as described inthe claims.

What is claimed is:
 1. A lamp head module comprising: an opticalmacro-reflector including a window having an outer surface; an array oflight emitting diodes (LEDs) positioned within the optical reflector,the array having a high fill factor and a high aspect ratio operable toprovide a high irradiance output beam pattern having a peak irradianceof greater than 25 W/cm² at a work piece surface at least 1 mm away fromthe outer surface of the window of the optical reflector, wherein thepeak irradiance does not require operation of the array at a pulsedemission duty cycle; and a micro-channel cooler operable to maintain asubstantially isothermal state among p-n junctions of the light emittingdevices at a temperature of less than or equal to 80° Celsius, themicro-channel cooler assembly also providing a substrate for the array,wherein a thermally efficient connection is formed between the array andthe substrate by mounting the array to the micro-channel cooler whereindeep and long coolant flow channels in fluid communication with themicro-channel cooler serve to balance flow of coolant through themicrochannel cooler.
 2. The lamp head module of claim 1, wherein thearray is directly mounted to the micro-channel cooler.
 3. The lamp headmodule of claim 1, wherein the micro-channel cooler maintains asubstantially isothermal state among the p-n junctions at a temperatureof substantially less than or equal to 45° Celsius.
 4. The lamp headmodule of claim 1, wherein the LEDs are electrically paralleled.
 5. Thelamp head module of claim 4, wherein at least one of the LEDs is anultraviolet emitting LED.
 6. The lamp head module of claim 5, wherein anaspect ratio of a width to a length of the array is substantiallybetween approximately 1:2 to 1:100.
 7. The lamp head module of claim 6,wherein the aspect ratio is approximately 1:68.
 8. The lamp head moduleof claim 5, wherein the peak irradiance is greater than or equal to 100W/cm² and the work piece surface is at least 2 mm away from the outersurface of the window of the optical reflector.
 9. The lamp head moduleof claim 1, wherein a plurality of the LEDs are connected in series. 10.The lamp head module of claim 1, wherein microchannels of themicro-channel cooler that are closest to a bottom surface of the arrayare in thermal parallel across a shortest dimension of the array. 11.The lamp head module of claim 10, wherein coolant flow through themicrochannels is substantially balanced.
 12. The lamp head module ofclaim 1, further comprising a flex-circuit, bonded to the micro-channelcooler, the flex-circuit operable to individually address the LEDs orgroups of the LEDs.
 13. The lamp head module of claim 1, wherein themicro-channel cooler is clamped between one or more cathode connectorsand one or more anode bus bodies to facilitate factory replaceability.14. The lamp head module of claim 1, further comprising: a flex-circuit,including a patterned cathode layer, to independently address aplurality of groups of one or more LEDs of the array; a thermallyconductive lamp body having opposing thin outer walls and having formedtherein deep and long coolant flow channels in fluid communication withthe micro-channel cooler; and wherein the deep and long coolant flowchannels serve to balance flow of coolant through the micro-channelcooler.
 15. The lamp head module of claim 1, further comprising:integrated LED drivers; a thermally conductive body; and wherein theintegrated LED drivers comprise a plurality of metal core printedcircuit boards (MCPCBs) mounted to opposing sides of the thermallyconductive body and wherein the plurality of MCPCBs are conductioncooled through the thermally conductive body.
 16. The lamp head moduleof claim 1, wherein the optical macro-reflector is field replaceable.17. The lamp head module of claim 1, wherein the optical macro-reflectorcomprises a right-hand half and a left-hand half each of which representa portion of an ellipse, each ellipse having two focuses, wherein thetwo focuses of the right-hand half have corresponding focal points thatare offset to the left of a centerline of an intended output beam andthe two focuses of the left-hand half have corresponding focal pointsthat are offset to the right of the centerline.
 18. The lamp head moduleof claim 1, wherein a plurality of the light emitting diodes areconnected in a series/parallel arrangement.
 19. The lamp head module ofclaim 1, wherein the optical macro-reflector comprises twonon-rotationally symmetric, non-transparent halves.
 20. A lamp headmodule comprising: a high aspect ratio monolithically bonded foilmicro-channel cooler substrate layer having a greater length than widthwherein deep and long coolant flow channels in fluid communication withthe micro-channel cooler serve to balance flow of coolant through themicrochannel cooler; a high aspect ratio light emitting diode arraylayer having a greater length than width mounted to the micro-channelcooler substrate layer, the light emitting diode array layer having ahigh fill-factor and comprising a p-n junction layer, wherein the highaspect ratio monolithically bonded foil micro-channel cooler substratelayer has formed therein a plurality of microchannels and those of theplurality of microchannels that are closest to a bottom surface of thehigh aspect ratio light emitting diode array layer are in thermalparallel across the width of the high aspect ratio light emitting diodearray layer; a flex-circuit layer, including a patterned cathode circuitmaterial layer and a thin dielectric layer, mounted to the micro-channelcooler substrate layer, the cathode circuit material layer separatedfrom the micro-channel cooler substrate layer by the thin dielectriclayer, wherein the cathode circuit material layer and the thindielectric layer combine in thickness to be less than 3× a thickness ofthe light emitting diode array layer; and an optical reflector layer todirect photons emitted by said light emitting diode array layer, theoptical reflector layer being at least 25× a thickness of the lightemitting diode array layer, wherein the thicknesses are measured in adirection substantially perpendicular to the p-n junction layer.
 21. Thelamp head module of claim 20, wherein the light emitting diode arraylayer emits incoherent light.
 22. The lamp head module of claim 20,wherein the light emitting diode array layer is connected to the cathodecircuit material layer via at least one wire, the at least one wireterminating in a connection to the cathode circuit material layer at apoint lying between the cathode circuit material layer and a bottomsurface of the optical reflector layer.
 23. The lamp head module ofclaim 22, further comprising a spacer layer between the opticalreflector layer and the cathode circuit material layer, the spacer layerhaving a thickness of at least a diameter of the at least one wire. 24.The lamp head module of claim 20, wherein the optical reflector layercomprises a macro-reflector having an entrance aperture and an exitaperture, the entrance aperture being at least as wide as a sum of awidth of the light emitting diode array layer plus 2× the diameter ofthe at least one wire but no more than 3× the sum.
 25. The lamp headmodule of claim 20, wherein the optical reflector layer has a centersection that is wider than either the entrance aperture or the exitaperture.
 26. The lamp head module of claim 20, wherein the opticalreflector layer comprises a macro-reflector having an entrance apertureand an exit aperture, the entrance aperture being at least as wide as asum of a width of the light emitting device array layer plus 2× thediameter of the at least one wire but no more than 5× the sum.
 27. Thelamp head module of claim 20, wherein the macro-reflector comprises aright-hand half and a left-hand half each of which represent a portionof an ellipse, each ellipse having two focuses, wherein the two focusesof the right-hand half have corresponding focal points that are offsetto the left of a centerline of an intended output beam and the twofocuses of the left-hand half have corresponding focal points that areoffset to the right of the centerline.
 28. The lamp head module of claim20, wherein: the optical reflector layer is separated from themicro-channel cooler substrate layer by the flex-circuit layer; and theflex-circuit layer is less than approximately 3× the thickness of thelight emitting diode array layer.
 29. The lamp head module of claim 20,further comprising a wire layer and wherein the optical reflector layeris positioned with respect to the light emitting diode array layer suchthat a bottom surface of the optical reflector layer is betweenapproximately a thickness of the wire layer and 1.5× the thickness ofthe wire layer above a top surface of the light emitting diode arraylayer.
 30. The lamp head module of claim 20, wherein the light emittingdiode array layer is connected to the cathode circuit material layer viaat least one electrical conductor, the at least one electrical conductorterminating in a connection to the cathode circuit material layer at apoint lying between the cathode circuit material layer and a bottomsurface of the optical reflector layer.
 31. The lamp head module ofclaim 30, further comprising a spacer layer between the opticalreflector layer and the cathode circuit material layer, the spacer layerhaving a thickness of at least a thickness of the at least oneelectrical conductor.
 32. The lamp head module of claim 20, wherein theoptical reflector layer comprises a macro-reflector having an entranceaperture and an exit aperture, the entrance aperture being at least aswide as a sum of a width of the light emitting device array layer plus2× the thickness of the at least one electrical conductor but no morethan 3× the sum.
 33. The lamp head module of claim 20, wherein theoptical reflector layer comprises a macro-reflector having an entranceaperture and an exit aperture, the entrance aperture being at least aswide as a sum of a width of the light emitting diode array layer plus 2×the thickness of the at least one electrical conductor but no more than5× the sum.
 34. The lamp head module of claim 20, wherein themacro-reflector comprises a right-hand half and a left-hand half each ofwhich represent a portion of an ellipse, each ellipse having twofocuses, wherein the two focuses of the right-hand half havecorresponding focal points that are offset to the left of a centerlineof an intended output beam and the two focuses of the left-hand halfhave corresponding focal points that are offset to the right of thecenterline.
 35. The lamp head module of claim 20, further comprising anelectrical conductor layer and wherein the optical reflector layer ispositioned with respect to the light emitting diode array layer suchthat a bottom surface of the optical reflector layer is betweenapproximately a thickness of the electrical conductor layer and 1.5× thethickness of the electrical conductor layer above a top surface of thelight emitting diode array layer.
 36. A lamp head module comprising: apackage including: a high aspect ratio array of light emitting diode(LEDs), the high aspect ratio array having a greater length than width;a flex circuit having a segmented cathode layer to which bond pads ofthe high aspect ratio array are electrically coupled; and a high aspectratio monolithically bonded foil micro-channel cooler having a lengththat is greater than a width and providing a substrate surface to whichthe high aspect ratio array is mounted; and a lamp body having formedtherein an input coolant fluid channel and an output coolant fluidchannel, wherein coolant fluid flows from the input coolant fluidchannel through the micro-channel cooler and to the output coolant fluidchannel to remove waste heat from the high aspect ratio array, wherein alength and a width of the input coolant fluid channel and the outputcoolant fluid channel is substantially similar to the length and thewidth of the high aspect ratio monolithically bonded foil micro-channelcooler, respectively, and a depth of the input coolant fluid channel andthe output coolant fluid channel is at least one third the length of thehigh aspect ratio monolithically bonded foil micro-channel cooler andwherein the input and output coolant flow channels balance the flow ofcoolant through the microchannel cooler.
 37. An ultraviolet (UV) lightemitting diode (LED) curing system comprising: a plurality of end-to-endserially connected UV LED lamp head modules each including: an opticalmacro-reflector including a window having an outer surface; a LED arraypositioned within the optical reflector, the array having a high fillfactor and a high aspect ratio operable to provide a substantiallyuniform high irradiance output beam pattern having a peak irradiance ofgreater than 25 W/cm² at a work piece surface at least 1 mm away fromthe outer surface of the window of the optical reflector, wherein thepeak irradiance does not require operation of the LED array at a pulsedemission duty cycle; and a micro-channel cooler assembly operable tomaintain a substantially isothermal state among p-n junctions of LED inthe LED array at a temperature of less than or equal to 80° Celsius, themicrochannel cooler assembly also providing a substrate for the LEDarray, wherein a thermally efficient electrical connection is formedbetween the LED array and the substrate by mounting the LED array to themicro-channel cooler assembly wherein deep and long coolant flowchannels in fluid communication with the micro-channel cooler serve tobalance flow of coolant through the microchannel cooler.
 38. A lamp headmodule comprising: an array of light emitting diodes (LEDs) having ahigh fill factor and a high aspect ratio operable to provide asubstantially uniform high irradiance output beam along a long-axis ofthe array, wherein the LEDs include one or more ultraviolet emittingLEDs; a high-aspect ratio micro-channel cooler assembly, including amicro-channel cooler portion and outer capping layer portions, operableto maintain a substantially isothermal state among p-n junctions of theLEDS, the high-aspect ratio micro-channel cooler assembly also providinga substrate for the array, wherein a thermally efficient electricalconnection is formed between the array and the substrate by mounting thearray to the high-aspect ratio micro-channel cooler assembly; wherein athickness of a heat spreader layer of the micro-channel cooler portionis less than approximately 200 microns; wherein a width of themicro-channel cooler portion is approximately 1.1 to 1.7 times a widthof the array in a shortest dimension of the array and wherein deep andlong coolant flow channels in fluid communication with the micro-channelcooler serve to balance flow of coolant through the microchannel cooler.39. The lamp head module of claim 38, wherein the array is directlymounted to a top surface of the micro-channel cooler portion.
 40. Thelamp head module of claim 39, wherein a vapor phase oven is used toreflow solder thereby mounting the array to the top surface of themicro-channel cooler portion.
 41. The lamp head module of claim 40,wherein the solder is lead-free.
 42. The lamp head module of claim 41,wherein a tacky flux is used to tack the LEDs in place prior to placingthe high-aspect ratio micro-channel cooler assembly in the vapor phaseoven.
 43. The lamp head module of claim 38, wherein the thickness of theheat spreader layer is less than or equal to approximately 125 microns.44. The lamp head module of claim 38, wherein the width of themicro-channel cooler portion is approximately 1.2 times the width of thearray.
 45. The lamp head module of claim 38, wherein: the array includesat least one LED in the shortest dimension of the array; themicro-channel cooler portion includes a plurality of internal channelsrunning in the shortest dimension of the array and substantiallydirectly under a bottom surface of the array; and each of the LEDs arecooled in thermal parallel.
 46. A lamp head module comprising: a packageincluding: a high aspect ratio array of light emitting diodes, whereinthe high aspect ratio array has a greater length than width; a flexcircuit having a segmented cathode layer to which bond pads of the highaspect ratio array are electrically coupled; and a high aspect ratiomonolithically bonded foil micro-channel cooler having a length that isgreater than a width and providing a substrate surface to which the highaspect ratio array is mounted; a lamp body having formed therein aninput coolant fluid channel and an output coolant fluid channel, whereincoolant fluid flows from the input coolant fluid channel through themicro-channel cooler and to the output coolant fluid channel to removewaste heat from the high aspect ratio array, wherein a length and awidth of the input coolant fluid channel and the output coolant fluidchannel is substantially similar to the length and the width of the highaspect ratio monolithically bonded foil micro-channel cooler,respectively, and a depth of the input coolant fluid channel and theoutput coolant fluid channel is at least one third the length of thehigh aspect ratio monolithically bonded foil micro-channel cooler andwherein the input and output coolant flow channels balance the flow ofcoolant through the microchannel cooler; and wherein the package isaffixed to the lamp body.
 47. The lamp head module of claim 46, whereinthe high aspect ratio array is directly mounted to the substratesurface.